MSExcel Problem

I work as a Customer support engineer. Recently i faced the following problem in a customer’s machine. i need help urgently.
The system is an AMD Athlon processor based on a VIA Motherboard with 128MB RAM. The problem reported was that Excel quit after giving a memory error. This was faced only by excel and no other office application had this problem. Reinstallation of Office2K solved the problem but only temporarily, the fix lasted 2 days. Next I reinstalled Win2K (Over-write previous installation) and Office2K. The problem resurfaced after some 5 days. Then I tried a full format of the HDD, and OS & Office installation. Worked for a few days but excel conked off again.
Any ideas, anybody?
cheerio
Vivek