No cart release? Bummer...
G7400's won't work in the U.S. unless you have the right equipment, or know how to mod the console. First you need a converter for the Euro power plug and voltage. G7400's also have Euro-style RF plugs, which aren't compatible with any U.S. video input that I know of. And, since G7400's output a PAL signal, you need a TV or video card capable of handling PAL.
I've heard that G7400's can be modded for composite video, but I haven't seen any plans for it anywhere. There are also some G7400 models that have an SCART connector, which might be a better solution for the video problems, but they seem to be rather scarce.
If you're looking for the G7400 BIOS or ROMs, Digital Press has some
here.