I have faced such many Times, but in my case its the DMA which is culprit.
XP disables it , everythind is slower.
Following is the mechanism that has worked for me, please try it at your own risk, it involves modifying the registry:
1) Open RegEdit
Find the following KEY: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\ Class\{4D36E96A-E325-11CE-BFC1-08002BE10318}\000x
The last four digits will be 0000, 0001, 0002, 0003, and so on.
Under each key, delete all occurences of the following values:
MasterIdDataChecksum
SlaveIdDataChecksum
Reboot the computer. Windows will now redetect DMA settings.
2) try other thing
clean windows\prefetch folder
and run bootvis , in that - tools -> optimize system
download bootvis:
http://drjimit.googlepages.com/bootvisdownload