256 is kind of the bare minimum to run OS X
Currently in Opera I have 64 tabs open, IE 7, MSN Live and a bunch of other crap, and this computer isn't slowing down at all with 1GB of RAM. Maybe try adding some more RAM or using some real browsers![]()
All of our macs at work have at least 1 gig of ram if not more. Of course they are used for special purposes though like 3D rendering, digital audio, video editing, graphic design, etc.
heck one of the highschools in my school district has a freaking render farm, and all the work stations are dual G5s with 2gig of ram running Maya.
It also involves the sites you are visiting too. Having a text only page, a flash page, a video stream page, etc.. you get the picture. This could also be one of the reasons too. However, an upgrade (if possible on a mac, I don't know cause I don't use one) of the memory should help out.