There's an excellent author out there, Brian Greene, who had a series on Nova and has a few books out right now on this subject, for about 10$ each. Check your local book store for Elegant Universe and Fabric of the Cosmos (I think that's the name). He specializes in dumbing this stuff down for the normal people among us.
As for the 5th dimension...what about the 8th? or the 9th? You can have as many dimensions as you want as long as they mathematically make sense. Trying to understand them, however, is a whole 'nother ball game. <-- paraphrased from Elegant Universe.