My understanding is (and I haven't tested this out yet -- probably should have!!) that you can "try" the on-line system free. It will not let you actually file the taxes without paying them. The price they charge for on-line filing seems to be something like US$10 less than the price they would charge for selling you the software (that price is, BTW, tax-deductible!
I'm not sure if you can file electronically if you are not a US resident. I was planning on using the on-line service if it seems secure; if not, I'll download the regular TurboTax program and pay the software licensing fee, use it on my own PC, and then probably copy all the figures onto the forms by hand (because my printer isn't working; not their fault.)
I've been using this program for quite a number of years now and I'd never do US taxes without it again. But a simple 1040EZ might not be such a hassle. In my case I've got to do Schedule "C" and I have quite a few sources of income as I'm a freelancer, so it gets more complicated.