Logic 5 is PC/Win & Mac, (also you would qualify for the $299 upgrade to L7) You can find it on eBay fairly cheep... and is still a good product... you just don't get some of the cool new toys... but you could still use it on the mini, boot from an externel FW400 drive, to speed the system up and use the internal drive for audio, or vice versa... always better to use two drives for Logic.
Been using Logic at my G/F's house on her stock mini without too much of a problem.
Still my G5 is better for it, the mini can hold it's own... I recomend freezing audio whenever possible for the mini.
I would also recommend 7.1 not 7.2 for the mini. 7.1 install disc is $29 from apple.