Some ambulances run a BLS unit with two EMT's - some run a ALS unit with 2 paramedics - and some are starting to run with 1 paramedic and 1 EMT. With the latter - you'd better enjoy rolling code 3 everywhere because that's all you're going to be doing. You'll be the driver. You won't get any real hands on experience besides taking vitals when you first get there. BLS units mostly transport from one hospital to another or pick up minor (ahem, VERY minor) patients or 5150's (people going in for psychological evaluations). I agree with OldMan that your best bet will be going for an Emergency Department Tech job. You'll get a lot of hands on experience because they'll work you very, very hard. The downside to becoming a full time EMT in either situation is the fact that it's difficult (at least here in the Bay Area) to live on an EMT salary ($10-$12/hour) when rent is $1500/month.
The skills you'll learn are invaluable especially since you'll be able to carry on the secondary examinations and general medical knowledge to medical school. Honestly, however, I learned much more in my upper division physiology class than I learned in my EMT class - but it all depends on what you want. Having and keeping up your EMT certs will look good on any job application - but just make sure that it's something that you want to do and not just something you're doing to look good on a resume (or med school application).
Good luck.