I have all of my music on my computer loaded as a library on my laptop, as well.
The way to do that would be to set up a mapped hard drive, which is basically like a virtual drive. Find the network address of the other computer, and navigate to where your music is stored, and map a network drive to it. This will make those files appear to be on your other computer, as well. Then you can open iTunes on the computer, and add files to library. Add the folder that your other music is stored on. Make sure to deselect any copying options or organizing options, you only want one version of iTunes to handle the renaming of files.
Note: when you add new music to one library, it wont automatically add to the new library. Just remember. Also, transferring to the iPod over the network takes a really long time. Don’t do this if you want to transfer thousands of songs, it will take hours. If you are going to transfer lots of songs, its best to physically be at the computer.
Otherwise, you might as well just copy songs to both computers.