Slow on Outlook 2003

I am running Outlook 2003 on Windows Xp service pack 1 with 1GB of RAM and more than 5GB free hard disk space.

I had almost 900MB of outlook personal store file(pst). My computer performance degraded after working on the outlook for a short while. I ran ?scanpst.exe? to scan for error on the pst file.?Surprisingly, each time the program detects some error and prompted for repair. I follow the instruction to repair it and the resultant end up the performance of the system had a drastic improvement!!!

I shall run this utility every now and then in order to keep up the system performance. Do you have any idea what is the bottleneck of the above issue?