that USB drive will work very well with his, soon to be acquired, Intel iMac.
If there is nothing on it that he cannot live without, it may be advantageous to format the drive as Mac OS Extended (journaled).
If there is stuff that he would like to save, copy it to the new Mac and then format the external as above.
My father-in-law may be jumping ship and going from his PC to a new Intel iMac. He asked me whether the external USB 2.0 hard-drive he currently has connected to his PC will work on a Mac. I could not tell him because I've only dealt with Firewire-connected hard-drives on my Mac. To split the question even futher, if the USB drive works when the Mac is booted in PC mode, will it work when in Mac mode?