URL: hxtp://search.yahoo.com/search;_ylt
Infection: JS:ScriptPE-inf [Trj]

So is this telling me that yahoo.com search itself is infected or what?

Hello,
end of address you posted suggests that it was page with results from search. I think it was one of pages found by yahoo that show this warning and not yahoo itself.

Possible. Anyways. If Avast! is warning you about that site, putting an active link to it is not good. I’ve reported the link to a mod to be disabled

It’s simply telling you that you used yahoo search to reach an infected site.
The site is infected not the tool used to reach it.