Ben, I use a couple of different spread sheets, which works for me. But remember when storing loads of important data on computer; you should make regular back-ups in both magnetic media and hard copy format (ie save them to disk/CD and print out the information on a weekly; at least; basis.
That way, should your computer 'die', you still have the information. If you wanted to be ultra safe, I believe there are web-sites you can save your spreadsheets too; at minimal cost.
Alternatively, George systems sell a package for around £50 which often gets a good press on this site. Click on the search function at the top of the screen and type in 'George'.