I got this great tip from Popular Photography Magazine. . .
I’m just copying and pasting here. . .
More Megapixels for Bigger Prints?
Q: The pixels are visible when I make prints over 12×18-inches from my 6.3MP camera. Do I need to get a camera with more megapixels to make bigger prints?
A: Before you go shopping for an upgrade, try setting your camera to shoot RAW, not JPEG. Then convert those files to TIFFs, use Adobe Photoshop’s Image Size (set to Bicubic Smoother) to upsize, and then sharpen while viewing your photo at 50%. Chances are your prints will look pretty good when you check them out at least six inches away.