Howdy,

All of these suggestions are good, however if you just want to save your scan as a .jpg right now without having to add more software, do this.

Scan the picture and save it. Open it with your browser right click on the picture and go to

Save Picture as...
Then
Save as Type...
and choose .jpg

A simple and quick work around.

Instead of PhotoShop, you may want to think about Image Ready. Same company, but specifically for putting graphics on the web/screen.