your good, the 5 speeds are pretty robust. The only weak link is the clutches. People run the 1.8t up to 300whp on the stock tranny(not sure if they reinforce anything though). My 1.8t has 192k miles and the transmission shifts pretty smooth.
If you want more information I would go to
www.audiworld.com and look through the b5 a4 FAQ or
www.quattroworld.com and read some of the posts there or search for what you want.