First open up Registry Editor go to this location...
HKEY_LOCAL_MACHINE->System->CurrentControlSet->Session Manager->Memory Management. In there find SecondLevelDataCache. There enter the size of your cache in decimals. So if you have a Athlon because the size of L2 cache is 256KB, enter 256. For a Duron, enter 64 for 64KB.

Disable Paging Executive
In normal usage, XP pages sections from RAM memory to the hard drive. We can stop this happening and keep the data in RAM, resulting in improved performance. Note that only users with a large amount of RAM (256MB+) should use this setting. The setting we want to change to disable the ’Paging Executive’, as it is called, is called DisablePagingExecutive. Changing the value of this key from 0 to 1 will de-activate memory paging.

System Cache Boost
Changing the value of the key LargeSystemCache from 0 to 1 will tell Windows XP to allocate all but 4MB of system memory to the file system cache, basically meaning that the XP Kernel can run in memory, greatly improving it’s speed. The 4MB of memory left is used for disk caching, but if for any reason more is needed, XP allocates more. Generally, this tweak improves performance by a fair bit but can, in some intensive applications, degrade performance. As with the above tweak, you should have at least 256MB of RAM before attempting to enable LargeSystemCache.

Input/Output Performance
This tweak is only really valuable to anyone running a server - it improves performance while a computer is performing large file transfer operations. By default, the value does not appear in the registry, so you will have to create a REG_DWORD value called IOPageLockLimit. The data for this value is in bytes, and defaults to 512KB on machines that have the value. Most people using this tweak have found maximum performance in the 8 to 16 megabyte range, so you will have to play around with the value to find the best performance. Remeber that the value is measured in bytes, so if you want, say, 12MB allocated, it’s 12 * 1024 * 1024, or 12582912. As with all these memory tweaks, you should only use this if you have 256MB or more of RAM.Win2k/XP Shutdown Fix:First of all open RegEdit, if you dont know how do do this its simple Go to Start,
click on Run (should be in the bottom right hand side) and type Regedit.

Navigate your way to HKEY_LOCAL_MACHINE then ---> SYSTEM then --->CurrentControlSet then --->Control
Click on control and in the right window you will see this key WaitToKillServiceTimeout

It should be set to 20000, what this means i do not know, but lower it to 200, i did this safely with no problems.Make XP Browsing faster:This make broswing a lot faster, but if you use scheduled tasks, don't do this, Open up the Registry and go to :

HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/Current Version/Explorer/RemoteComputer/NameSpace

Under that branch, select the key :


and delete it.