You can purchase a R72 IR filter and shoot through it. Your exposures get extremely long. It basically cuts visible light out and only lets in some IR. There is enough to get the "IR" effect. A cheaper way is to find some old unexposed and developed slide film. You can double up the "Black" exposures, put it between the lens and body and shoot IR.(not the best suggestion because it could add dust and debris inside the camera when you expose) If you have a p&s, you can put the doubled up film in front of the lens, but you will still have very long exposures.
Dug