yeah you can, when you come back though make sure you take your drivers lisence and another form of id such as a birth certificate or social security card. they will just warn you to next time you need a passport.
Dont listen to the majority of these people (sorry).
If you are traveling by car, no you do not need a passport UNTIL January of 2008. At this time passport requirments are only for people traveling by air in & out of the US.