largeSystemCache

3. Set the value to either 0-Disable, 1-App launch prefetch, 2-Boot Prefetch, 3-Both ("3" is recommended).
4. Reboot.
It will decrease the boot time but double and increase the performance of your XP. Try it!
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\SessionManagerMemory Management -> LargeSystemCache
When enabled (the default on Server versions of Windows 2000), this setting tells the OS to devote all but 4 MB of system memory (which is left for disk caching) to the file system cache