Since things are getting worse, there's a few things I can recommend (I
may have made these before, I don't remember), in the order I'd try them:
1) You can try opening it in OpenOffice and doing a SaveAs. I've had
success with this at times. My current favorite flavor of OpenOffice is
NeoOffice:
http://www.neooffice.org/
Version 1.2.2 was just released today - I've used the previous builds
with no problem.
2) Do the same thing using WinXL2003, which has better error correction
(though I've not had nearly as much success with that).
3) Create a fresh workbook. Copy the contents of the errant workbook to
the new one. Do NOT move sheets from one workbook to another, instead
use Copy/Paste. Don't copy entire rows or columns. You can paste, then
Edit/Paste Special/Formats if all the formats don't come through.