I'm running GTalk on Windows 7, and it refuses to work properly with Alt-Tab.
Let's say I've got 2 message windows open (msg1 and msg2) and the contact list, as well as Firefox. Alt-tab from Firefox to msg1 works, but now the contact list is the most recent thing in the alt-tab list (not Firefox as expected). Then there's the problem that I can't use alt-tab to select a specific message window, and when switching back to msg2 (showing msg2 in the alt-tab window) it might switch back and have focus on msg1.
I found this thread complaining about the same problem, but it's over a year old, and I'm hoping some progress has been made.