When you use Windows Update to perform an Express or Custom installation of Windows XP Service Pack 2, the installation halts and you do not receive any error message.
If you inspect the contents of the %SystemRoot%\Svcpack.log file, you see entries similar to:
150.782: There is not enough space on the disk.
150.782: Service Pack 2 installation did not complete.
150.782: Update.exe extended error code = 0x70
This problem will occur if you do not have sufficient free space to download and expand the SP2 files.
NOTE: You must also have at least 30 megabytes of free space on the System partition, the one that contains Boot.ini, NTLDR, and Ntdetect.com.
To workaround this problem, free up disk space by running Start / All Programs / Accessories / System Tools / Disk Cleanup.
You can also temporarily reduce the space used by System Restore, temporarily reduce any excess space you configured in Virtual Memory, and / or compress little used folders.