This album, along with Mike's here: http://forums.audiworld.com/tt/msgs/1557717.phtml covers how to replace a ball joint on the Audi TT (2000-2006).

Parts list:
- 2 Ball joints: p/n 8N0 407 365 A superseded by 8N0 407 365 C
These are available at your favorite Audi parts counter ($140 each) or online source like www.1stvwparts.com ($78.96 each) or www.autohausaz.com ($53.60 each).
- 6 hex nuts, shouldered M10 p/n N 103 320 01
- 2 shouldered hex. nut, self-locking M12X1 p/n N 908 088 01

A specialty tool needed is the ball joint puller, available at www.mytoolstore.com/toolaid/suspn02.html ($15.50).