Since i'd suggest to not use the emulator at all, it doesn't matter so much. The SDK is available for Windows, Linux and Mac OS X so you can pretty much go with anything you want. My current development machine is an Asus EEE PC 1215n, a netbook (i have a monster desktop as well, by the netbook is somewhat more comfortable). I run Windows 7 32-bit/Ubuntu 10.10 (dual boot setup due to a couple of other things i'm doing not related to Android). It works like a charme. The emulator will be dog slow though, no matter how beafy your machine is, so i suggest getting an actual Android device.