A P166 would be fine. A high-end 486 (100-133MHz or so) would probably do okay too. Just make sure you have enough HD space for the dev tools you want (might want to be careful to get a system than can handle drives > 528MB, as this was a common BIOS limitation in older systems). Topping it off with RAM might not be a bad idea either (particularly if you're going to be compiling stuff), but it depends on the chipset... I'm told that some just turn off the cache once you pass a certain amount...