Thanks for the replies. The 2009 comes with a 640 gig 7200 rpm HDD, so I thought migrating might work better than just swapping drives since I want to keep that faster drive as the boot drive. Besides, I'm a little fuzzy on the consequences of booting a current-model Mac Pro from a drive that had been used in a 32 bit machine. Seems like migrating the old computer stuff to the new drive might be cleaner, as long as that's possible to do without adverse consequence.
As to iLife, I already have the disk (had to shell out for '09 since the version that came with the original Leopard wouldn't work under Snow Leopard).