no multi touch gestures under osx with that trackpad besides the scrolling, and the two finger secondary click. and i second the linux thing, it basically jsut treats it as a tablet. I first discovered this when i installed an osx virtual machine on my mac, and it thought my built in trackpad was a tablet, then it clicked!! haha
BUT, if you do get a magic trackpad I highly recommend better touch tool, you don't know the true pleasures of your mac, of the magic trackpad till you get BTT installed
EDIT: as for the ram thing, your computer will do page ins and page outs automatically, and as far as I know... there is no limit to size (in windows its limited by the pagefile size, which you set, or live with the defaults) it just grows dynamically as needed.... its not exactly doubling your ram, but it somewhat allows you to use more than what you have. but for your computer ddr2 ram is pretty cheap for 2 gigs, you can even go nuts and get 4 🙂