Mini mixer/headphone amp with mp3 input for practice

[spargo]

I have a POD 2.0 that I use for practice on occasion with headphones.  Before that I had a Floor POD Plus.  What I miss from the floor pod (and find ridiculous that it's not in the POD 2.0) is an additional line input for CD/MP3/computers.  It was great to be able to play some music through my computer or phone and play my guitar along with it in my headphones.

I'm looking to build a little box that will take either the headphone or line out from the POD 2.0 and an output from an MP3 player or computer and be able to mix them so I can hear both at once.  Separate volume controls are not absolutely necessary since the POD has output volume and the other device will as well - but if volume is included that's fine.  It would be MOST preferable to have a passive box.  I'd think this would be possible since I'm basically taking two headphone outputs and combining them.  The POD input will be mono, and the mp3 input and output will be stereo.

Any ideas for a passive solution?  If not, how about powered?  I'm thinking maybe a variation of the mini mixer.

[artifus]

if using a computer why not a software mixer? pod out to soundcard line in with the added bonus of being able to record your performances.
a simple passive mixer should work fine too. google is your friend.

[derevaun]

You might get away with using a Belkin Rockstar or similar, as long as there are no giant impedance mismatches.