Disable windows messenger.

Start -> Run -> Type service.msc -> Double Click on Messenger- Stop


To increase system performance

Right click my computer. Click properties.
Click advanced.
Click settings (under performance).
Click Adjust for best performance.
Scroll to the bottom and check the last one “use visual styles on windows and buttons”.


These Settings will fine tune your systems memory You need at least 256MB of ram to do this

Go to start\run\regedit -and then to the following key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management
1.DisablePagingExecutive -double click it and in the decimal put a 1 - this allows XP to keep data in memory now instead of paging sections of ram to harddrive yeilds faster performance.
2.LargeSystemCache- double click it and change the decimal to 1 -this allows XP Kernal to Run in memory and improves system performance a lot.
3.Create a new dword and name it IOPageLockLimit - double click it and set the value in hex - 4000 if you have 128MB of ram or set it to 10000 if you have 256MB set it to 40000 if you have more than 512MB of ram -this tweak will speed up your disckcache.
Reboot

XP holds files in it's memory even after you have closed the application using them making it impossible to delete them from your harddrive.

Start -> Run -> Regedit
Find the HKEY_CLASSES_ROOT\SystemFileAssociations\.avi\shellex\PropertyHandler\ directory and delete the "DEFAULT" key.

Disable Services
XP Pro runs a lot of services by default that are pointless if your not on a corporate network, the following services are ones that I safely disable thereby freeing up memory but check what each one does first to make sure your not using it for something:
Go to Run and type services.msc, right click on each service, properties and choose disable.
Alerter
Application Layer Gateway Service,
Application Management
Automatic Updates
Background Intelligent Transfer
Clipbook
Distributed Link Tracking Client
Distributed Transaction Coordinater
Error Reporting Service
Fast User Switching Compatibility
IMAPI CD-Burning
Indexing Service
IPSEC Services
Messenger
Net Logon
Net Meeting
Remote Desktop Sharing
Network DDE
Network DDE DSDM
Portable Media Serial Number
Remote Desktop Help Session Manager
Remote Registry
Secondary Logon
Smartcard
SSDP Discovery Service
Telnet Themes
Uninterruptible Power Supply
Universal Plug and Play Device Host
Upload Manager
Webclient
Wireless Zero Configuration
WMI Performance Adaptor

Disable Error Reporting - Windows XP
1) Right Click on my Computer -> properties
2) Click on Advanced tab
3) Click on the error reporting button on the bottom of the windows
4) Select Disable error reporting
5) Click ok, ok again.

Hope this helps.....!