http://www.google.com/search?hl=en&q=disable+disk+space+low+warning&btnG=Search
oh look! a wikihow
oh look! a wikihow

Quote from: http://www.wikihow.com/Turn-off-the-Low-Disk-Space-Warning
1. Run the Registry Editor (REGEDIT.EXE).
2. Open HKEY_CURRENT_USER\ Software\ Microsoft\ Windows\ CurrentVersion\ Policies\ Explorer.
3. If it's not there, create a DWORD value and call it NoLowDiskSpaceChecks.
4. Double-click on NoLowDiskSpaceChecks, and enter the value 1, and press OK.