EPS (Encapsulated PostScript) is a file format that is able to hold both bitmap and vector information. For a full explanation, look here:
The EPS file format
You can see a handy guide to all graphics formats here:
Graphics file format summary - Wikipedia, the free encyclopedia
Regarding your other question: if you mean you want to produce a vector image from a bitmap, there has been another thread about this recently. Have a look at this:
http://forums.biorust.com/adobe-phot...matically.html (Getting a vector from a bitmap automatically?)