I've been scanning receipts (for insurance purposes) in and save as PDF files, then burning them to a CD-R, and then locating the CD-R out of my house. PDF files are as cross platform (linux, mac, and peecee) so I'm guaranteed compatability.
If my house burns down, or someone steals all my originals, I'm set to file a claim.
Anyway, my tools for this: I picked up a cheap Acer scanner ($30 after rebate), and i'm using Photoshop 5.5, which isn't cheap but does save to PDF, but you could also get PrintToPDF, which is a cheap way to create PDF files. I guess you could store them on a zip or multiple floppies if you don't have access to a CD burner.