This one is the best tweak for windows XP I ever found, and it works very well. With this tweak we will force windows to load kernel and drivers in memory.
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.
That’s it, enjoy your faster pc 
