i would use a notebook, a multi out audio-
interface and 'ableton live' as software.

you could also trigger backtracks by some
sampler software like native instruments kontakt
that you can use standalone.
kontakt can play tracks direct from harddisk, so
it doesn´t matter how long they are.
you would have to prepare click tracks though.

or use a hardware harddisk recorder for the
backtracks and the click, and a roland spds
for live-triggering additional samples.

decode

Easiest way to do it, Ipod + DI Box

think of it as 2 channels instead of left and right

channel 1, click.
channel 2, mono audio

djrr3k wrote: Easiest way to do it, Ipod + DI Box

think of it as 2 channels instead of left and right

channel 1, click.
channel 2, mono audio

+1

A slightly different suggestion: pick up a second-hand Roland VS880, or something similar. (its a portastudio style 8 track HD recorder / mixer).

The backing tracks could then be in stereo if you want, while still allowing a separate click track.

Another useful bonus: playback can be started with a footswitch, and the VS has an option to automatically stop playback at each locate point. In other words you can start each song by stomping on a pedal, and at the end of the track the VS will stop playback automatically and wait for you to cue the next song with another stomp.

And if you turn off the data compression it will probably also sound better than an Ipod

of course the VS880 also has a 1/4" headphones socket built in, and can send the click track to the cans while sending your stereo mix to the aux outs. ;)

Ipod/laptop and DI is the best way to go.