Heater core replacement, I'm doing it.
 

Unfortunately my heater core is indeed kaput. No amount of flushing or CLR can fix the fact that the two pipes coming through the firewall have a crack the entire length of them. They leak coolant under the hood and I tried heat-shrinking, super-glue, sealant, nothing. The core will have to be replaced and I'm jumping in head first with close to 0 experience.

Is there any advice from someone that's done this? Specific tools I'll need?
I've read that manuals don't provide correct instructions on some parts.
Also, from what I understand, it's really just a labor-intensive issue, nothing is that "tough". If you know what youre doing and exactly what to do next, it will only take 4-5 hours of unscrewing things. In reality it takes 8-12 because everything must be done in the right order and finding bolts/screws is tough.

I'm fine spending a weekend and nights after work doing this to get it done, what I ABSOLUTELY DO NOT WANT is to be missing a tool or piece and have to sit around for a week for it to come in the mail.

Thanks for any help!

Did you watch the 3-part youtube video from the guy who did it recently? Looks heinous. :)

This is the first one:
Youtube should show you links to the following ones on the right.

Do you have the special bolt to remove the steering wheel? I have one and I can say that it's almost impossible to find in a store, you have to buy it online. (I used ebay.) It's not clear from the video if you really to remove the steering stuff, he says later that he's not sure.

There's also this: AudiWorld Tech Articles

Yeah I've watched those videos (as well as a number of others) quite a few times. Honestly every time I do I just get nervous about starting. I'm just going to have to jump in.
I don't have an special tools but I have a buddy who works for Audi that says I need 8mm, 10mm 13mm and torx. Plus two "keys" that get the radio out. He also says "don't take the steering wheel off. Pull the drivers seat and unbolt the steering column and lay it on the ground."
I'm guessing that's going to make it a little harder at one point but save me a much of time in the end.

Taking the steering wheel off is super easy if you have the bit. (It's not a torx, it's a "12 point" aka "triple square".) As long as you have a week or so to wait for it in the mail, this is the exact one I got and it's perfect:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=281165530346
Honestly I'd get it just so you have it if you need it. And search youtube for "a4 steering wheel removal" for a brief video with some tips. (Be sure to mark the gears with a marker before you finally slide it off.)

I've also removed my radio with the radio keys in the past to install an ipod adapter, and I have to say that was a HUGE pain. I think I could do it again faster now, but jeez I was tugging on that thing for an hour before I found the proper angle and correct strength to pull it. It didn't help that I bought cheap keys that cut through my hand as I pulled. Get keys with nice plastic grips so that it's easier to pull hard. Or, perhaps you don't even need to pull the radio, I think the youtube guy said that he though he could have skipped pulling it.

EDIT: I should add: in my case this is a 2001 A4 1.8T. Not sure how consistent the bit is across all B5's but according to the docs it seems to be.

I'm getting conflicting reports saying it's either a T55 or a triple square.

It's very easy to find out, wouldn't take more than a few minutes. You just unscrew the two torx behind the wheel and lift up the airbag carefully. You don't even need to disconnect the battery unless if you're paranoid, since you don't need to unplug any wires to check. Just lift the airbag up and you'll see the bit staring right at you and you can check what it is.

Caveat: assuming your wheel is the same or similar to my wheel, can't vouch for any others. :)

Depending on the year of your car, it could also be a 24mm bolt, mine is.

For the later cars, I've always used a T55 torx (I believe that's correct..) to remove the wheel without a problem.

I've order a small set of torx and a small set of triple square bits along with my core. Those, along with a set of radio keys and the decent sized crescent tool set I have should be enough.
The new core gets here near the end of this week or beginning of next. At that point I'll jump in and try to update this thread with my progress and pics (and inevitably ask thousands of questions).

you are gonna need 4 radio keys. ebay