Those two machines are very, very different. I'm not sure if they have one port in common.
But anyway, if I were you, I would invest in an external hard drive enclosure with USB2/FireWire. Remove the 7500's hard drive, place it in the case, and plug the case into the iMac. I'm not sure if you can see a system 7 disk on OS X (never tried it), but I know you can see an OS9 disk. You could do what you like from there.