|Well that could be caused by any number of things without knowing what the specific error codes or messages are. Have a look in the Event Viewer just after you've tried to use MM and see if it shows any more information about why it's had to close.|
General tips which may help:
1. Defragment the system drive.
2. Error check the system drive.
3. Run the System File Checker on the system drive.
All three of those utilities are built in to Windows XP.