I think you'll find that while almost any flatbed photo scanner will "do the job" of scanning B&W prints, the advantage you'll get with buying a reasonably good scanner, Hortense, is both better scans and better software with the scanner.

Thus, you might be well served by something like the Epson 3200, or the current enhanced model, the 4870. If possible, try to find one that has the SilverFast software (which works as a Photoshop plug-in) bundled with it. Without good scanning software and a fairly good image-editing package (e.g. Photoshop or PaintShop Pro), you'll have a hard time matching the quality of the scan to that of your print.

I have a brief article on my site that discusses the basics of scanning. You might find it helpful.

http://www.rbarkerphoto.com/scanning-tutorial.html