Sometimes ADSL issues can be caused by faulty inside wiring. Some of this can be because the wiring is poorly done, and it really isn't hard to take care of on your own (instead of having a technician dispatched, which can cost several hundred dollars for an ISP or ILEC technician to come out and rewire the house).

First, you will need these tools/equipment (should be easy enough to obtain from an electronics store):

• 66 block (come in various sizes or types -- most likely the 25-row block with each row common should be plenty) -- Also, grab a few screws to mount it.
• Optional: mounting hardware for the 66 block -- will keep your wires neat.
• RJ-11 crimper + two connectors + scrap wire -- scrap should be small enough to be crimped -- like a pair of wires from some Cat5 cable (or, buy a standard telephone cord and cut it in half -- may not work as well, or may be harder to work with)
• Female-Female inline coupler (RJ-11)
• Punchdown tool for the 66 block -- or, a screwdriver (flathead) - "jewelers" screwdrivers work really well, or needlenose pliers.
• One DSL line filter
• Wire cutters/strippers
• 3M Scotchlok connecters (the red kind -- UR or UR2) are very useful in doing splicing if you need to... or to reconnect wires, like after removing the half-ringer. Also pretty cheap -- about $.15/connector. Well worth it for the performance you get. You can use pliers to crimp them, but there are specialized tools for it.
• MAYBE extra wire, depending on your current inside wiring (cat3/cat5 will do fine, or if you have other scrap around -- it doesn't matter -- all you need is one pair)

To rewire your home:

1. Safety first, unplug your line from the NID (the telco uses about 40VDC, which is kinda tingly, but if someone happens to call while you're doing work, that's about 80VAC/60Hz. Ouch.) While you're at the NID, if you haven't already done so, cut out your half-ringer. You don't need to, and it won't cause any serious issues being there, but it can't hurt either. It's useless, but sometimes degrades the DSL signal a bit.
2. Find the pair that comes into your location from the NID. Most likely there will be a junction with a pair leading to each telephone. Sometimes, three wires are used, but only the red and green matter -- the yellow doesn't matter. You may have a single wire leading in series to each telephone -- if this is the case, you'll need some of that spare wire, and run a line directly to the location where your DSL modem is plugged in -- I'll leave that up to you.
3. Find the pair that your DSL modem is on -- one possible way (if you don't have any fancy test equipment) is to open up the wall plate and short out the red and green terminals -- don't worry, your phones aren't plugged in, right? Then, go to the location where your lines converge, and use a continuity tester to find that pair. Also, check to see if anything is spliced in on this line, it can be painful if it is... Most likely, your best bet if something is spliced, disconnect the DSL modem's pair from that splice, and run brand new Cat3/Cat5 to it.
4. Mount the 66 block in a convienent location.
5. Take the pair from the NID, and push the red wire onto one of the rows, and push the green wire onto a different row. (They should not be shorted out!)
6. Connect the pair that goes to the DSL modem directly to the same rows as the red/green.
7. Take the two halves of a phone wire, or use your crimper to create two "halves" of a line, and push these down onto the red/green rows as well. Note, when looking at the RJ-11 connector from the side with the pins, red is the second pin, green is the third (from left to right) -- this may or may not matter.
8. Attach the RJ-11 end to the coupler, and plug your DSL filter into the other side of the coupler.
9. Attach the other half to the other end of the DSL filter, and punch the wires down across about 5 rows apiece (depending on how many phones you have). Be sure not to short out any connections, once again.
10. Begin reconnecting each of the lines individually -- cut off any bare wire, and punch the pair down onto the corresponding rows.
11. Tuck the wires in neatly and make sure everything looks clean and is securely punched down.
12. Remove any old DSL filters (except for the one you just installed).
13. Finally, reconnect the line at the NID, and test all your phones (checking for any other splices on the same line as the DSL modem -- trust me, you'll hear it -- an unfiltered line sounds VERY noisy).
14. Make sure your modem syncs up, and everything there is working as well. If something isn't, double check all your connections, and that everything is punched down. It's possible (but unlikely) that a wire was severed somewhere along the way, so if it STILL doesn't work, check to see that the wire is still intact. If it isn't, run a new pair.
15. As a final check, power cycle your modem and then have your ISP run an MLT and check noise margins. You SHOULD see an improvement, and hopefully the rewiring removed any issues that you may have had before. Note, when asking to run an MLT, don't call from the same line as your DSL service -- they aren't able to run the MLT with the line in use.

Some pictures (a before/after thing without the before):

These were the old screwposts the original Bell install from the 50s used. Yellow wsa connected to the earth ground (cold water pipe) from the black wire you see here. Red and green were on the left/right respectively.

This shows an example of how I rewired everything. Coming into the 66-block on the left side, the red and green are on the first/second and third/fourth rows. From there, there's the homerun to the ADSL modem (the cat5, orange-white and orange lines), as well as the DSL filter (not really shown, but goes into the inline coupler, and to the dsl filter. This then returns from the filter, and spreads out across five rows of the 66-block (I left one row between the line coming in and the rest of the lines to the house, and even have a few spare spots. My wiring below isn't so great, but it works. As a note, the old dark brown lines were through the nail sticking down, and tacked into the wood -- it was NOT fun to remove. If you have this issue, it's probably best to just cut off the wire, since removing the tacks without damaging the wire is very difficult...

That's all, hope this helped!

-dougk_ff7