Strange Word 2000 problem

I have a user that created a document in Word 2000, then emailed it to someone else with Word 97, who made changes to the document and emailed it back. The document will now not open properly. Word hangs for a bit then generates an error and exits. With Task Manager open and on the performance tab, the CPU jumps immediately to 100% and available memory continues to drop until the error which closes Word. I did manage to get it open on my system once, but when I tried to save it, I got an out of memory error. Any ideas would be appreciated.