Q: eMac upgrade

Yes.

No. eMacs are PPC machines. You cannot run Snow Leopard on them. Leopard is most likely the end of the OS X line for that model. But as I recall you can no longer run Mac OS from within Tiger or later, but you should be able to dual boot between Mac OS and Leopard by installing each on separate partitions.

Kappy wrote:

But as I recall you can no longer run Mac OS from within Tiger or later,

Very nearly correct. You can run OS9 in Classic emulation from within 10.4 Tiger but not from within 10.5 Leopard.

However, only the first eMacs with Nvidea graphics can boot into OS9. All other can only do Classic emulation. To see which of the eMac variants you have, use this Apple article and let us know:

http://support.apple.com/kb/HT2395

My 1 GHz eMac (ATI Graphics, USB 1.1, Combo drive) can boot into 9.2.2, 10.4, or run OS 9 in Classic emulation from within 10.4.