I've posted this many times as this subject seems to confuse people for some reason. This came directly from Audi HQ :
"All power enhancements are excluded from the Audi warranty system. In fact any item not approved by Audi UK has the same warranty disclaimer; the official terminology is' any non approved item will not be covered by Audi warranty or any part affected by its fitment'. Under trading standards and retail legislation, any centre supplying a non approved item should inform the customer in writing on the invoice that a) it has been requested by the customer and b) the implications of the factory warranty."
Since Distiller, you haven't said what country in or filled in your profile (hint hint) it's hard to give acurate information. (I'll assume your in the UK)
Abt are a warrantued supplier in Germany but NOT in the UK for performance parts. Audi centres can however fit body kits etc.
Beware of any one telling you the warranty is unaffected. This is wrong. Some dealers offer their own but this is not an Audi UK warranty. Watch the misleading dealers squirm when you ask for it in writing! /ubbthreads/images/graemlins/smirk.gif