There are a handful of people who are successfully running ProTools on a 64 bit system. None of them are using a firewire interface. ProTools LE on 64 bit is beta at best.
If you're just getting started, you may just want to buy a decent interface with an LE version of some software. The Presonus stuff comes with Cubase AI which is (apparently) 64 bit compatible. Studio One is a purchase on it's own probably near $400. What is your budget?