I have a pair of old eMacs, one of them is running Tiger, the other one is running Leopard. I think you'll love Tiger. That is one of the best, if not the best desktop OS ever made. It's simple, it's quick and it offers so much in terms of usability. I'm not keen on Spaces, Time Machine and the other Leopard additions, so if I could, I'd put Tiger on more of my computers. Sadly, newer MBPs are unable to run Tiger and I also need RapidWeaver, which requires Leopard or Snow Leopard.
In case you want to keep both OS, get an external Firewire hard drive that you can boot from. Replacing the HDD in the eMac is such a pain that many users just get one as there is hardly any difference in speed.
Anyway, do a clean install and tell us about your experience! One more thing - when browsing the internet, you might want to try a few Flash solution or workarounds. These older machines are not particularly good on Flash, but check out dozens of threads about the subject.