You may have tried many tweaks like modifying windowsXP start-up applications, prefetches, unload DLLs method,etc. And yes those methods do work for me.
I have just accidentally found out another way to give you an extra boost in windowsXP's boot performance. This is done by disabling your unused devices in Device Manager.
for example, if you don't have input devices that are connected to one of your USBs or COM ports, disabling them will give you an extra perfromance boost in booting.
Yes i've tried this. I've disabled every devices that currently has no use for my pc and it worked great. My booting time is much faster than before.
Go to Control Panel -> System -> Hardware tab -> device manager
Disable devices that you don't use for your PC and then restart. Good luck!
SO: I think that this article could go into more detail or point to one that does.