Look, face the fact that PowerPC is dead. It's a bit like having a PC from 2000, they really have no use. I myself have a dual 2005 G5, and even IT struggles at YouTube. Software out of date, no security updates, and slow. There is NO reason whatsoever to use a PowerPC mac (unless it is a quad G5) at this day and age, unless you have no other computer or if you have a use for it such as a light file server. Why even ATTEMPT video editing on a mac that is maybe 10+ years old? I understand if you can't afford a new mac, but honestly if you can't, you really have no business video editing on a computer that is so old. If you can't afford a new mac, buy a PC, and if you insist on using OS X you can Hackintosh it relatively easily.
Don't avoid the facts. I suggest he sells the eMac and uses it to help save up for a PC to Hackintosh.
I only use my G5 for mucking about with, downloading stuff, or playing old games/legacy software. Even my 10 year old younger brother thinks the G5 is really slow, he only uses it for Word and VERY light web browsing.
To answer your question it is useless or slow at most things.