There is no emulator that plays them all, as far as I know. There is a very shitty 7800 emu, and from what I remember a decent 5200. If I were you I wouldn't bother with anything but the 2600 emulation. Use Z26 for that.
http://www.zophar.net/windos.phtml You can find all the emulators at Zophar.
A word of warning if you decide to try the only 7800 emu there is: it's a bitch to get it to work right. I can't remember how I did it, either.
[ 11 July 2001: Message edited by: adidas ]