I can't quite recall where I lifted this info from exactly - some tech site someplace... But all in all its good, solid advice for Windows XP:

1. Disable all sounds in windows - To disable all Windows XP task sounds go to Start, Control Panel, Sounds and Audio Devices, select the "Sounds" Tab, under "Sound Scheme" select "No Sounds".

2. Disable auto load for all devices (CD-ROM/DVD Drives/CD/DVD-RW drives, etc.). Right click on each drive and select “Properties”. Select the Autoplay tab. For each Content Type, click “Select an Action to Perform” and choose “Take No Action”.

3. Change Processor Scheduling to Background Services go to Start, Control Panel, Advanced Tab, click the Settings button under Performance, Advanced Tab, change Processor Scheduling to “Background Services”.

4. Always Use DMA on Hard Drives Make sure that your hard drives are correctly using DMA for low CPU overhead. Open Device Manager and expand the entry labeled 'IDE ATA/ATAPI Controllers'. Right-click on each IDE channel entry, and select the Advanced Settings page. Here you can check that the Transfer Mode is correctly set to 'DMA if available'.

5. XP will create a file named hyperfil.sys to store the contents of your RAM before going to sleep. If you want to use Hibernation (like on a laptop), leave it checked.

6. “Always On” Power Scheme - go Start, Control Panel, Power Options, Power Schemes Tab. Set Power Schemes to “Always On” and the Turn Of Monitor, Turn Off Hard Disks, and System Standby settings to “Never”.

7. Disable “Indexing” and Compression go My Computer, right click on the C: Drive and select Properties, make sure “Compress Drive to save space” and “Allow Indexing Service…” are NOT checked. Repeat on audio drives.

8. Static Page File Size- Set a static page file size to 1.5x the RAM you have or 512 MB Max. Tweak - Go to "Start", "Settings", "Control Panel", "System", "Advanced" Tab, in the "Performance" section select "Settings", "Advanced" Tab, in the "Virtual Memory" section select "Change", change the "Initial Size" and "Maximum Size" to the same size then select "Set" and "OK".

Notes - If you are getting low memory errors then you need to add more RAM to your PC. Increasing the Page File to accommodate the low memory situation should only be considered a temporary solution. Using additional Virtual Memory over System RAM will reduce performance. It is a good idea to have at least 512MB-1GB of RAM in a PC today. A simple test to determine if you need more RAM is to use you PC for a whole day without rebooting, then look at the Task Manager (Ctrl-Alt-Delete), Performance tab. If the "Commit Charge - Peak" is ever higher then the "Physical Memory - Total" your system could benefit from adding more RAM.

9. Reduce Recycling Bin Drive Space Usage In Windows XP the Recycle Bin is set at default to reserve 10% of your hard drive, this can be a big waste of drive space. To change the Recycling Bin Size, right-click on the "Recycle Bin", left-click on "Properties", select the "Global" Tab, then "Use one setting for all drives". Move the slider to "3%".