roders

Garageband Latency

I've been playing about with Garage band & my guitar, plugging my guitar directly into my Mac (with a 1/4 Cinch jack to mini jack lead to plug in) in Audio midi setup I've changed the input (and output) sampling rate to 24Bit, but when I change the input as well as output smalping rate to 96000 Khz (to reduce latency) I get problems.
I can only set either the input or the output to this resolution (not both at the same time, which ever I set first seems to stick, and then whichever I set second doesn't) or I get a click and the resolution immediately sets back. If for some reason the resolution change does stick in Audio Midi setup. As soon as I open Garageband I hear a click, and if I check Audio Midi setup, the resolution has gone back down again.

What I want to know is, is they're a workaround in the OS? Is it a bug in the OS? Is it a limitation of Garageband? Or do I need a separate Audio interface?

P.S Garageband is set to low latency in the prefs and only one audio channel is active/monitored.

Hardware/Software versions

Macmini Core Duo 1.66Ghz 2GB ram, upgraded 7200 rpm internal laptop drive.
Mac OSX 10.5.4 Leopard, Garageband v3

Using A Griffin Imic With Osx 10.2.5 &/or Logic

I can get audio out of my Griffin iMic from my 12" G4 PB, (system sounds, iTunes/Games etc) but plugged into the input of the iMic I have a Behringer V-Amp (guitar Amp/FX simulator) with my (obviously guitar plugged into that).
Under system prefs/SOund The iMic is selected for output and Input, and under Input, the input level meter registers a signal when I play soemthing on my Guitar, but I hear nothing from my amp/speakers (connected to the output of my griffin iMic).
If I plug my Behringer V-amp directly into the Mic socket of my 12" G4 PB and my amp/speakers into the headphone out I can hear my guitar (when I change everything to Built in audio under system prefs/audio) but not when everything is plugged into the iMic (although all audio produced by, not routed into my Mac is audible through my speakers).
I've noticed that under "Audio Midi Setup" Playthrough needs to be selected for me to monitor my guitar's audio when everythings plugged directly into my Mac, but this option is greyed out (unselectable) for the iMic.
Can anyone monitor an input when it's plugged into a Mac via the iMic under OSX 10.2.5?
Also, I'm getting no audio/level in Logic 5.5, even though it can see and I have selected the iMic as my audio device, I've got the iMic working in logic before too, just can't quite remember how I did it.
I checked Griffins Support section on the iMic but it's pretty out of date and only refers to useing it with 10.1, which handled audio differently, but it mentions soemthing about playthrough being greyed out under OS9, and having to use an ASIO driver (not available for OSX yet).
Can anyone help me out with this as I'm dying to make sweet sweet music with my 12" PB G4!