Yeah sure it can be done!
Of course it is best to have the highest quality / highest resoloution sources possible, but if "what you have is what you have" then thats that!
Best case scenario is that you can get a real mastering guy to do it, but sometimes DIY is the only way....
The goal of mastering in my mind is, you are trying to find a balance for all the material within a certain context... That context includes, the tonal balance and relative prerceived volume of the parts within a song, that song compared to the one before it and after it, the Album as a whole, and the ultimately the album compared to EVERY OTHER (great sounding) ALBUM EVER MADE.
Its kind of a huge context to keep in mind and in balance, but that is the goal.
You want to make it so that the listener never have to touch the EQ / volume of stuff while listening to your record as a whole, and also as they put another album on after listening to yours...
If you are thinking about doing it yourself, I would buy this book:
Mastering Audio by Bob Katz
I hate it when people tell you to "read a book" but its a big subject.
I would say that if you arent going to buy the book, at least sit down and do a bit of free reading about it online.../
http://en.wikipedia.org/wiki/Audio_mastering
http://www.tweakheadz.com/mastering_your_audio.htm
http://www.soundonsound.com/sos/aug04/a ... tering.htm
Even if you are going to pay someone to do it, it will pay off to have some understanding of the goals of the process, and a vocabulary for dealing with the engineer.
Houlihan... you going to do it yourself?