400Mhz PPC G3? Is that a PowerMac G3 tower, an iMac, or something else? In any case, that thing's got a day or two of age on it...
Also, as another Mac user, what's your opinion on the current version of Transmission?
iMac DV/SE Blueberry, a truly beautyful machine from the past XD . I had to force the installation of Tiger server on it, as it's not officially supported (target mode-install from iBook G4-yay) and you can tell it's forced given that the iChat server dosen't want to start

Transmission... not exactly my piece of cake. However i have to admit that it's main competitor, BitRocket lately got left behind, and that as a simple and eventually even "noobish" client, it works. Still, i don't like it

the fact that it dosen't have a web interface means a lot for me, given it will actually hit the resources of the computer i'm using, instead of another one on the lan, so in my case, it can be at best a client to download a couple of files i don't want to queue on Azureus. Also try BitSticks out,
http://www.vanillasoap.com/widgets/ more for the lulz than anything serious, but it's based on the official BitTorrent and from my single test it used no cpu (like 0.5% on the G4 iBook) but it could've been a case.