We have a lot of spreadsheets (xls) in our source code repository. These are usually edited with gnumeric or openoffice.org, and are mostly used to populate databases for u
Do you use TortoiseSVN for doing your commits and updates in subversion? It has a diff tool, however comparing Excel files is still not really user friendly. In my environment (Win XP, Office 2007), it opens up two excel files for side by side comparison.
Right click document > Tortoise SVN > Show Log > select revision > right click for "Compare with working copy".