hooking up external sources to my new laptop - help!

I just bought a new laptop. (It's a Toshiba M30X, if that helps - I got it for cheap over Thanksgiving weekend.) It has a Mic In jack, but no Line In. I'd like to be able to plug in external sound sources; for instance, to burn LPs or do home recordings. However, nothing I plug into the Mic In jack works. For instance: I tried plugging in my turntable using a Radio Shack preamp and a Y-adapter. This worked on my old desktop (and yes, I checked the preamp battery), but not on my laptop. No sound whatsoever.

I tried calling tech support to see if I was doing anything wrong. I suspect I got connected to a call center in India, to someone who didn't actually know the product. In any event, they told me that only a microphone would work with the Mic In jack. I don't really believe that, but could someone tell me if I'm doing something wrong, or if I need to buy a new sound card, or what?