For true cross-platform web conferencing, Cisco Webex is the only way to go. GotoMeeting only recently added OSX support, and Linux, forget about it?
My experience on getting it work with the built-in components on my Thinkpad... forget about it!
Ubuntu 8.0.4 worked sporadically and and on 8.10 Firefox crashed. Hard.
I Googled a bit and didn't find any quick workarounds, so I decided to try it the old fashioned way. So here is what I came up with to get it working reliably. I assume this works on other distros as well.
(All of this assumes you create another user for just webex so you don't corrupt your local .mozilla and .adobe files etc.)
1. Get the tarball of Adobe Flash (10.0.22.87 tested)
2. Download Firefox 3.x (3.0.8 tested)
3. Download JRE .bin installer (jre6u13-linux-i586.bin used)
4. Create a webex directory and move all of these to it
5. Uncompress them there
1. Remove ~/.mozilla and ~/.adobe
2. Run ~/webex-local/firefox/firefox then quit
3. Run the ./flashplayer-installer script
4. Run the java installer binary
5. Create the symlink for the java plugin within $HOME
ln -s ../../webex-local/jre1.6.0_13/plugin/i386/ns7/libjavaplugin_oji.so
1. Run your local firefox
2. Confirm you can execute java applets by visiting http://java.sun.com/applets/jdk/1.4/demo/applets/Clock/example1.html
3. Click on the test meeting http://support.webex.com/support/support-overview.html