No trimming of the dash should be necessary.
The DIN tools will work, but it'll take some time, patience, and possibly another set of hands.
I got my radio out via some coathanger pieces cut into "U" shapes (generic DIN tool). It took me about an hour by myself. It was definately a pain in the a$$.
For an audio newbie, I'd suggest getting the car stereo installation kit from
www.crutchfield.com. You'll probably have to call to get it. They're also the only ones who reliably supply all of the necessary hardward for bypassing the factory amp. Plus, their directions are vehicle specific and very helpful. They've also got tech support to walk you thru it.
-C