There are 3 tweaks you can make to change how XP uses memory.
Open Regedit and Find HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\
Disable Paging Executive:
XP pages data from RAM memory to the hard drive. We can stop this happening and keep more data in RAM, resulting in better performance. Users with a large amount of RAM (256MB+) should use this setting. The setting we change to disable the ’Paging Executive’, is DisablePagingExecutive. Changing the value of this key from 0 to 1 will de-activate memory paging.
Changing the value of the key LargeSystemCache from 0 to 1 will tell XP to allocate all but 4MB of system memory to the file system cache, allowing the XP Kernel to run in memory. The 4MB of memory left is used for disk caching, if 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 previous tweak, you should have at least 256MB of RAM before attempting to enable LargeSystemCache. Input/Output Performance:
This improves performance of large file transfers. If this entry does not appear in the registry, you will have to create a REG_DWORD value called IoPageLockLimit. The data for this value is in number of bytes, and defaults to Zero which equates 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. The value is measured in bytes, so if you want, 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. Use your hard drive less for Virtual Memory:
The Windows 98/ME "ConservativeSwapfileUsage=1" optimization does not work for XP.