Speed up windows by following these small tips

Disable remote services: If you never need to access the system over a network, nor have anyone else do so (for help troubleshooting a problem, for example), you can free up some Windows resources by turning these features off.

In Windows XP Pro, click
Start > Control Panel > System and Maintenance (in Category view) > System > Remote, uncheck the options under Remote Assistance and Desktop Sharing, and click OK (note that these settings aren't available in XP Home).
To disable these remote features in Vista, press the Windows key and type system, press the down arrow until System is highlighted, and press Enter. Click Remote settings in the left pane, and under the Remote tab in the System Properties dialog box, uncheck the option under Remote Assistance. In the Remote desktop section, click Don't allow connections to this computer, and click OK.
Disable remote-access features in the System Properties dialog box to improve Windows' performance.
Deactivate System Restore: If you prefer to use a backup method other than the one built into Windows, you can disable this feature. Just keep in mind that if you go completely backup-less, you'll lose data. Maybe not today, and maybe not next week, but someday. Eventually Windows and your applications will crash--guaranteed.
In Windows XP you can shut off System Restore by clicking Start > Control Panel > Performance and Maintenance (in Category view) > System > System Restore. Check Turn off System Restore, and click OK. Next, return to Control Panel and choose Administrative Tools > Services, click or double-click System Restore Service, select Stop, and close the window.
Disable System Restore in Windows XP by checking this option in the System Properties dialog box.
Do the same in Vista by pressing the Windows key, typing backup and restore center, and pressing Enter. Click Create a restore point or change settings in the left pane, uncheck your hard drive under Automatic restore points on the System Protection tab, click Turn Off System Restore at the scary warning, click OK, and close the Backup and Restore Center.