Try using "Save As" once and it should tell you where it thinks they're going.
Anything over 72dpi is a waste for stuff that you're only going to look at on a monitor. If you're scanning at 300dpi or higher, that's PRINT quality. You don't need or want that for email, or for the web.
And lordy, yes, save to .jpg rather than a bitmap!
One exception: .jpg is a 'lossy' format and it's not good for images you're going to manipulate in Photoshop, etc. For those, see if you can save to the native format of your tool (like .psd for Photoshop, .psp for PaintShopPro, and so on). Then export a .jpg when you're done.