Windows Vista includes a Disk Cleanup Wizard. To use the Disk Cleanup Wizard to free up space, follow these steps:

1. Click Start and then click Computer.
2. Right-click the drive you need to increase free space on, and then click Properties.
3. On the General tab, click Disk Cleanup.
4. On the Disk Cleanup Options page, click My files only or Files from all users on this computer. You'll clean up more disk space if you clean files from all users.
5.Scroll through the available options, and select the check box for anything you want to delete. If you're not sure, leave it.

You are safe removing the following files:

-Downloaded Program Files
-Temporary Internet Files
-Microsoft Error Reporting Temporary Files
-System error memory dump files
-System error minidump files
-Temporary files (close your programs first!)
-Per user archived Windows Error Reporting files
-Per user queued Windows Error Reporting files
-System archived Windows Error Reporting files
-System queued Windows Error Reporting files