I have the weirdest problem, for the last few days every hour or so (not exact) the clock jumps about back in jumps of 15 to 60 minutes and after some time the internet disconnects. i can reconnect the internet by unplugging and plugging back the network cable.
This is the second time this problem happens to me, the first time was when I installed VirtualBox. whaen I removed it the problem was gone. This time I have no idea what triggered it, the only thing I installed about the time the problem started was iTunes update (10.5.1) I tried removing it but the problem remained. (also tried to remove other programs i installed day or 2 before and it also didn't help) also, this is not a VM and currently I don't have any VM software.
since the solution is in the comments i'll write it here - apparently the windows time service got broken, this is the fix: http://technet.microsoft.com/en-us/library/cc738995(WS.10).aspx (run "fix it" from IE browser only)
The fix didn't work, about 2 hours passed and first the internet disconnected and then the clock jumped back...
This probably means that the problem is not only in the clock
A true solution was found, works fine for a day now! The problem was the small battery on the motherboard has run out!, it controls the internal clock. I replaced it with a new one and it's fine since.