best processor / configuration for MacPro and ProTools LE 7

[MH2006]

i want to buy a Mac Pro desktop machine. i'm considering just buying the cheapest one with a 2.8GHZ processor, 320GB hard drive and 1GB RAM and upgrading the RAM and hard drives myself. will the 2.8GHz quad-core be fast enough to run multiple stereo tracks with a bunch of plugins on each ? right now i'm on a MacBook Pro with a 2.3GHz dual-core intel and 2GB ram and it keeps maxing out the CPU and i'm friggin fed up. oh and will the lack of Leopard support be a problem? can i boot it using a Tiger installation?

any advice would be much appreciated. someone said to me that i should buy a cheap, faster windows box and hack it to run OS X but i'm afraid of the system being unstable and losing data.

thanks.