Have you narrowed it down to a specific folder or two or three?

My Vista's WinSxS folder has now grown to over 6.6GB's.

I read up some on this folder, but only enough to know not to go in there and start deleting stuff.

Its not a problem yet as I still have 20+ gigs free, but if it keeps growing at the this same rate (6.6 gigs in 2 months) - I am in for some trouble within a few more months.