When trying to fix online meetings with people around the world it can be quite difficult to find times that suit everyone.
Doodle is a great utility for getting people to agree times for meetings and it has introduced a time zone option, although it is a bit clunky.
If on the other hand you have decided to run a session at a particular time then I really like www.timeanddate.com, which has lots of utilities including one where you can fix a time and then send a link to all other attendees to allow them to find the time in their time zone. So the other day I set a meeting and sent this message to other people:
We will meet at 13.00 GMT Monday 24th November (see http://www.timeanddate.com/worldclock/fixedtime.html?month=11&day=24&year=2008&hour=13&min=0&sec=0&p1=0 for your time zone)
And they all could check their own time zones.
Things to watch with fixing meetings across time zones are: