Multiple prints on one sheet? Quick and easy way is to use the print option in Windows.
In W7, select the photos you want to print (Ctrl + left click on them to add several to the "print order") and click on the Print option on the toolbar. That will bring up a few options. Click on the printer you wish to use, paper size, quality and paper type. At the right of the window, there are several options (depending on paper size selected). For A4, these include Full page photo, 13x18cm (2), 20x25cm (about 10"x8") (1), 10x15cm (about 6" x 4") (2), 9x13cm (4), Wallet (9) and Contact sheet (35). Obviously, you'll get the best quality from a single image on each sheet but for cost effectiveness, I would suggest the 9x14cm option which gives 4 photos per A4 sheet. The 9 images you get per sheet using the Wallet option are (IMO) too small, although you could offer them as an option for people to buy!
It's a little more long winded in XP. Open the folder containing the photos to print then select the pictures to print. To the left of the window should be a panel with a box entitled Picture Tasks and in that box will be an option to Print the Selected Pictures. Clicking Next will bring up a fresh set of options - a set of thubnails with tick boxes. Select those you wish to print (or deselect those you don't) and click Next again. The new window now lists your Printing Options which is where you select the printer and (using the Printing Preferences button) set the paper size, type etc in the printer's driver window that pops up. Clicking Next (again!) brings up the Layout Selection window which has the same options as the W7 ones listed above but with an extra choice in the 10x15cm part - it allows you to print 3 on a page as well as the 2 option. However, if all the selected pictures are the same orientation, one of them will be on its side unless you go Back (using the Back button) and select a different picture in the other orientation. Not sure if that 3rd picture will be the right way up once selected - best to check - there's a Print Preview panel that shows what you'll get when you can (finally...) hit the Next (or Print, can't remember which) button to commit your final choice of photos to paper.
I haven't figured out a way to print the file names/numbers on each photo to make ordering easier but a minute or 2 with a Sharpie (or similar, although Sharpie do a silver felt tip to mark dark areas on photos) will name/number the display proofs.
Hope the above helps and isn't too confusing!
Nod.