How to print multiple images on 1 page
The easiest way would be to use Bridge. Go to the Output panel, select PDF, then select the 2*2 Cells template. Under Document, select you paper size you are printing to. Most likely you will want to leave Layout alone. Determine if you want any overlays (text/lables), a header/footer, or watermarking. Once you have the options you want, click the Save button at the bottom. Open the PDF that is created (the default behavior is to do this for you) and then print it from your default PDF reading application (Acrobat? Reader?).
Slightly more difficult is to download the Photoshop Optional Plug-ins (Mac: http://www.adobe.com/support/downloads/detail.jsp?ftpID=4965, Win: http://www.adobe.com/support/downloads/detail.jsp?ftpID=4688), install them and then you can use Picture Package. It does the same thing as the above Bridge steps only a PSD is created instead of a PDF (it is also more difficult to choose which files you want to use).