Disable Low Disk Space Notification in Windows XP

1.	Click Start, click Run, type regedit, and then click OK.
2.	Locate and then click the following key in the registry: HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer
3.	On the Edit menu, point to New, and then click DWORD Value.
4.	Type NoLowDiskSpaceChecks, and then press ENTER.
5.	On the Edit menu, click Modify.
6.	Type 1, and then click OK.

7. Logout.

From http://support.microsoft.com/kb/285107