Garageband Latency, Guitar Monitioring Options

[roders]

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

[houstonmusic]

I've done the 1/4 to 1/8 thing too, and i've never been able to get the latency to a low enough level that i was very happy with it. okay, but not really good enough. i do show my students how to do it though, just for the giggles of all those amp models and the ease of importing 3rd party midi tracks and playing along for study. (just drag a standard midi blues file, say, into the track window of GB and watch the tracks and correct instruments populate...)

that said, i've been using the line 6 tone port/gear box gold bundle for a while, and it's a much better solution. highly recommended.