Look in the a4 to m6 conversion sticky it has all the info you need. I have been told that you can run it with out a m6 tune but it will throw a ton of codes. I had mine changed before I started up the first time. If you don't get a reply about the wiring pm me with your e-mail and I will send It. I'm at work so can't do it now. I have a procedure for 1999 and up. 1998 is different some how I don't know that one.
in that long sticky there is a list of what you need to do with that bundle of cables that was on the shifter.
The car will run without the tune, just not very well. the RPM's will seem like they want to stay up and the speedo will be about halfway what it should be, so it would be worth it to find a tuner. Most shouldn't charge what they would with a full tune. I just dropped off my PCM at my tuner's shop and he swapped it over.