Here is what you have to do:
1) Open the regedit tool Start -> Run -> regedit.exe
2) Use the navigation in the left and go to HKEY LOCAL MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management
3) Double click the DisablePagingExecutive attribute, and put 1 in the decimal value field
This will make the drivers and the XP kernel run in memory.
4) Double click the LargeSystemCache attribute, and put 1 in the decimal value field
This will improve performance of the kernel
5) Double click the IOPageLockLimit attribute. On some later versions of windows XP that doesn't exists, so if this is the case you're done Otherwise you have to put to the hex value : 4000 for pcs with 128 mb ram, 10000 for 256 mb ram and if you have more put 40000. This value specifies how many bytes can be used for I/O operations in your system.
[Source: digg /gibberishtalk.com]