This isn't the best thing out there but it is another option.
Trillain is a PC OM program that allows you to connect to all of your IM accounts through one program.
There is a plugin for it called IM Everywhere that allows you to use your Trillian from a browser anywhere.
Trillain itself is $20 and all the plugins are free.
It does require a full time internet connection.
Trillian Pro is what you need.
I have used it on my other phones and I am playing with it on my new BB 7520. So far so good.
Not for the heavy IMer, IMO.