Guitar + Line In for practice?

[spargo]

I used to have a Floor POD Plus before getting into analog effects.  Now sometimes I use a regular POD 2.0 for practice with headphones.  But sometimes I wish I had the line input feature of the floor pod.  I could plug my guitar into it, and also my computer or mp3 player and play along with the music.  Unfortunately the POD 2.0 doesn't have this input.

Would it be easy to make a simple box to do this?  It would have a 1/4" input for my guitar and a 1/8" input for an mp3 player and combine the signals.  Maybe with a volume control for each as well if you want to get fancy.  It would be a basic 1/4" output that could then be sent to an amp, or in this case the POD that I can plug headphones into.

Has anyone done something like this, or is there an existing project?

[twabelljr]

How about something like this? Only install as many inputs as you need, 1-1/4" and 1-1/8", or a mix of 4 inputs in case you want to jam with a friend.  
http://www.generalguitargadgets.com/diagrams/mixer_sc.gif
The mp3 player has its own volume control also so you should be able to balance the levels easy enough I would think.