Mixing iPod and Computer Sounds?

This is an exploration of solutions. I don't have my perfect solution yet, perhaps somebody will help.

The short question is "what's the best way to combine the sound from my ipod and the sounds from my computer into one set of headphones?"

Here's the situation:

I've got an iPod which I sync with my work computer. When I want to tune out the noise of the office, I currently listen via iTunes. Windows handles the business of delivering music, new mail alerts and other system sounds to my headphones, with the volume set appropriately. However, the disk on my laptop is getting full. My iTunes library takes up almost half of the used disk space. So, I'd like to move the music to my home computer and I can bring the iPod with me to work.

Now, how to listen to the music while still being able to hear the alert sounds from my computer? If I had two sets of speakers, I could connect the iPod to one set and the PC to the other. This solution fails when I want to use headphones.

Possible options:

• External mixer - buy a small mixer and plug the ipod and the computer into its inputs, plug speakers or headphones into its output. The hardware volume controls for each input would be nice, but this solution requires a little desk space and an extra power outlet. There's also the matter of the "whoa, you're such a geek" factor when people see this extra box sitting on my desk. See what I mean by looking this Behringer model. That could be good or bad.
• Attach ipod to computer via line-in port - it's a simple idea, but I'm on a laptop with only a mono-mic input, and, once it's connected, I'm not sure what I would run to get the sound piped to the speakers. The mono-mic input is a deal-breaker. If I'm using a more compatible machine in the future, I'll worry about how the sound gets through the machine. Rogue Amoeba's LineIn looks like it would work on a mac.
• Fancy speakers - some speakers meant for computer use have two inputs and a headphone jack (such as these Bose speakers. Plug the computer into one, plug the ipod in the other. Seems pretty easy.

The speaker option is probably the best way to go, but I'm working on pure speculation as to how well this would work. This is why stores allow returns.