Which Mac?

Hello. I have a G4, once it had aged, i bought a P.C....bad move. The P.C. was unstable and has now stopped working [it took 6 months to fall.] I'm writing this on my 6 year old Mac G4. One of the great things with my G4, was that i was able to plug my guitar straight into the rear, i could record and use a load of effects through Garageband. I will be buying a new Mac, i want to plug my guitar/keyboard straight in and record/put them through effects. Should i look at a Mac Pro or can an iMac do it? What software do i need?
Thanks, Michael.

Any Mac with GarageBand will do it. You can use your soundcard as an interface if you've got the right cabling, or there are adaptors to take a 1/4 inch down to 1/8th inch which will plug right into the input.

Alternatively you might want to think about a proper interface, firewire audio interfaces are mega cheap these days and usually bundled with more software to play with! Check out the Line 6 Pod GX for example... Good sounds for not much money, and the ToneDirect monitoring is supposed to help with latency (not that I know for sure, I'm don't own any Line 6 gear personally)

Mac Pro is definitely overkill if you're just noodling - you'll find these at the core of pro studios running Pro Tools HD rigs, not really necessary for just a bit of fun and certainly not as portable (they're big heavy boys!) - maybe a Macbook would do you?

Hope this helps!