my Word 2003 is posessed!

I use Office/Word 2003 Pro in the home office to process documents on a weekly basis. The previous week's document is pulled up, and edited, sometimes rather heavily with large blocks being deleted and/or typed in.

Recently in the midst of deleting/editing, the document has begun taking on a life of its own, large blank blocks inserted, odd non-ascii characters, mostly square blocks, inserted. The document is at that point on it's way to infinity, is unsavable, unsalvagable.

First attempts to correct it, I rebooted the computer, then reinstalled Office. This weekend did a complete format - reinstall in WIN XP Pro. I've done a memory check, which turned up no errors, the hard drive has been re-partitioned and formatted, this time FAT32 - it formerly was NTFS.
The computer is a 2.4gig P4, with a 160 gig HD, 1.25 gig of ram, WIN XP Pro OEM.

Today, with a brand new windows and office installation - mid edit - the file went beserk again! :cry

Could a virus or other demon be hiding in the word document? Where to begin?
Thanks in advance.

p.s. I edited the same document this evening using Open Office without incident.

Sorry - just noticed that I posted this in the wrong forum. Someone who knows how (admin) feel free to move it.