1) what's the smallest wheel that will fit the B7?
2) what's the most inexpensive wheel that fits the above criteria
3) What's the best snow tire these days? I will be putting them on just for the trips to the slopes.

They know what they speak of. :)
(link is for those without TPMS)<ul><li><a href="http://www.tirerack.com/a.jsp?a=AR4&amp;url=%2Fsnow%2FWinterPackageMain.jsp%3F autoMake%3DAudi%26amp%3BautoModel%3DS4%2BSedan%26a mp%3BautoYear%3D2007%26amp%3BautoModClar%3DStandar d%2BModel">clicky</a></li></ul>