Turn an electric guitar into a bass guitar with garage band?

I'm a teenage DAW (is that the right term? A non-commercial person who uses software instead of hardware to record and mix?) and I am currently in the process of making my own cover for a song and writing my own songs. My questions are about an electric guitar (Ibanez Artcore AF75TDG) and amp (Roland Cube 30x). I am using a 17 inch MacBook pro. I also am using a USB M-audio MobilePre audio interface for my recording. I plug my acoustic guitar directly into the audio interface (I'm a bad boy... I need a DI box) and I have an OK mic for the amp I'm using (I would use one of the really BOSS condenser mics my dad bought, but I dont have mic cables in the house). I also have an M-audio "Key Studio" MIDI controller at my disposal. My questions are about the use of GarageBand:

1) How (hypothetically) do I plug my electric guitar into my MacBook Pro to take advantage of all the built-in amps in the software? Do I just create the track as an "Electric Guitar" track and plug into the audio interface normally?

2) I can do a bass line with my MIDI controller, but I want to try making my electric guitar sound like a bass guitar. Is there some way to do that? Like run the guitar through a software bass amp in GarageBand?

Please answer any way you like. If there is anything you think I need, please tell me. I can borrow equipment from my church (such as mic cables or SM57 mics, our DI boxes are pretty much shot now, but are still useable) if need be.

Thanks all.