The reason you're seeing them as TIFF is because you're shooting in TIFF. You need to change your camera settings if you want JPEG instead. ;-)
If you're in any of the record (shooting modes) and press your FUNC key, you'll get to more options on the smaller mono display (White Balance, ISO sensitivity, Image Quality and Image Size).
Available Quality settings include Basic (JPEG), Normal (JPEG), Fine (JPEG), and Hi (TIFF). You probably have it set to shoot in Hi (TIFF). Set it to Fine if you want JPEG instead and are willing to sacrifice the small quality differences.
If you already have photos shot in TIFF, most image editors will allow you to choose JPEG when you use their Save As option.
Irfanview (as eric s mentioned) is one popular editor that can convert your TIFF files to JPEG.