Video Conference Tool

does anyone know an open source video conference tool, that also runs on lower systems?

let's start with the topic now:

is there a possibility to create a mobile video conference tool? i think, skype rockz, but the problem is that you cannot hold a video conference without any plugins... furthermore skype's system requirements are too high for a little older computers... my girlfriend has problems with a skype video call on an intel pentium III mobile with 1 ghz, but she can't tell me how much ram... nevertheless there are some disadvantages of skype and lookin' forward to an alternate with lower system requirements and the possibility to hold video conference...

i think a nice tool is the "logitech videocall" software... i began today my 30 days trial together with my girlfriend and we were surprised how great it works... wihout any connection problems, no quality losings and the possibility to use nice features during the call... it's a pity that this service does cost 6 $ per month after the trial period... and now i'm lookin for an alternative...

i found no topic before, but i saw one about google talk...perhaps is there a possibility to create a video plugin for google talk or gaim?!

thank you!