Hibernation: If you don’t use this feature very often or not at all, then check to see if it has been disabled, as a hibernation file size is about the same size as the amount of ram/memory installed in your computer.
Windows XP Service Pack 3: If you have installed Windows XP Service Pack 3, look for an odd folder name which is located here C:\WINDOWS\SoftwareDistribution\Download\cf8ec753e88561d..........\ Note: the apparent random set of letter and number may vary from my example above but whatever the name is, it will be more than 600MB in size and can be safely deleted.
C:\WINDOWS\SoftwareDistribution\Download folder: You may see a number of folders or files located in here in addition to the SP3 folder mentioned above. Windows Updates uses this folder so after you have installed all the updates currently available from Microsoft the files (not the folder) contain in the download folder can also be deleted. Keep an eye on this folder as it can grow in size very quickly depending how you use your computer. It’s not uncommon to see anywhere from 200MB on up to 3 or 4GB of files located here. For example using a Windows XP SP3 CD to do a fresh (Clean Install) of Windows XP and just downloading and installing all the Windows Updates available since SP3 was released resulted in more than 295MB of folders and files.