Scan Disk is a useful tool for checking the integrity of your hard drive(s). If you have been hunting for Scan Disk in Windows XP you have probably found it missing. That is because its fuctions have been relocated into Explorer. Select the disk drive that you want to scan in Explorer, then go to the file menu > properties > tools > check now. The same procedure applies for Windows 2000.
Defragmenting your disk from time to time is also a good idea to keep the speed of access to your files at an acceptable level. When files become fragmented (split into different parts and stored on seperate areas of the disk) you may find that your computer slows down.