The main advantage of TIFF, or other uncompressed formats (like PSD), is there is no degradation of the imaage from the compression. With JPEG, there is additional image degradation each time you save the image (and reopen).
If you work with JPEGs, make sure you 1) do all your editing in TIFF (or PSD) and save ONCE as a JPEG when you are completely finished with your editing, and 2) save the original JPEG so you can start with the best possible image in case you want to do further editing later.
The main disadvantage of TIFF is the large file size (Hard disk space is cheap and getting cheaper!).
I would also add that scanning your own images is a pain, but you will have far greater control and improved quality. The Nikon film scanners are great!
Dave
G5 2.5 GHz Quad, 6.5 GB RAM, NVIDA 7800 GT Mac OS X (10.4.5) MacBook Pro 2.1 GHz