I've got a locked Barton 2500+ running at 11*200, stock voltage, running at 1:1 with Corsair XMS 3200
Trying to get it a little higher, but it needs some crazy voltages to get above 2.2 Ghz
Actually, I had the exact same problem. It had to do with the StyleXP skin I was using. If you're using Style XP, try changing skins, or disabling it altogether.
f.y.i.
I'm using the Milk "Cream" Skin, and it gets along just fine with firefox ;)
If you're using SP2, the problem is most likely a divx install. Same thing happened to me. As soon as I uninstalled divx the problem went away.
...waiting for a new version of divx...