Digi-Scene

I bought a brand new iPod a few weeks ago (a sweet 80GB iPod classic) and I'm having a devil of time figuring out how to get all of my music from the iTunes on my two computers onto the iPod. Long story short, whenever I sync with my work computer's iTunes, it wipes out the songs from my home computer. I want to MERGE the two, not overwrite them. Why isn't merge an option? I'm sure this is something simple but I can't seem to figure it out.

This is probably my karmaic come-uppance for laughing at Boni and his cell phone issues...