Excel 2003 SP3

I want to check data before and after it has been migrated between 2 systems
- and prove it has survived intact - using a checksum or similar.

Each dataset could be a range of numeric fields, eg telephone numbers, or
text data eg postcodes. Ideally each column would have a checksum at the
bottom which could be compared across 2 (or more) spreadsheets.

Any help greatly appreciated.