300 DPI is the absolute minimum resolution to get near photo quality prints at the standard 6 x 4 size on home gear. If your printer software has it, switch on the image optimiser. Set printer quality to the finest you can and use the best quality gloss photopaper you can afford. Increase to 32 bit colour in display properties. Try scanning at 300 DPI into your imaging software then "fit to page" in print preview and test print. If your printer is up to it you may get a passable result. If you do, you will obviously get better results at smaller sizes. If not you will need to get a printer that can handle at least 600 DPI, particularly if you want to enlarge to A4.If you use the largest DPI you have on the scanner, I hope you have alot of RAM, a fast CPU and big fast video card, otherwise manipulation can be a painfully slow experience. After all this, you can get adequate repro at 200 DPI if you have a newer "photo" type printer. All the top names (Epson, HP, Canon etc)all have "photo" settings that produce passable results from quite low resolutions. Down load the latest driver from your scanner and printer maker. The one that comes on the installation disc or Windows is very often about three revisions behind and this can make a big difference. Good imaging software can make things easier also. I use PhotoImpact V6, it's pretty good, Paint Shop Pro is OK but not as intuitive.
http://www.shortcourses.com has good background info about scanning, digi photography and printing, our site is
http://www.kaistech.iinet.net.au and may give you some inspiration.