Just another thought - if you're into gaming on line, did you ever download and install an in-game chat program called XFire?
We got rid of all the other cr*p off my son's PC and it still ran like it was submerged in treacle - i.e. it took ages to load stuff, but once loaded it seemed fine - except for internet where it was a good 50% slower than the other PC sitting alongside it on the same network.
We ran Hijack This! and discovered a load of similar files listed which didn't seem to relate to any other application on the PC. A bit of digging on Google identified them as XFire Files. We uninstalled it and then plodded through the registry deleting all other references to it and the dodgy filename.
Now runs like greased lightning.
Hope that helps
ST