Yes, sorry I saw it too late. Anyway I assure you it works. On your computer's sound settings you choose your sound card as default, and every sound will go on your speakers. Then in Teamspeak you can choose between the sound card and logitech headset as output and input. You choose the headset and it works, TS in headset and other sounds in you speakers.
Now, I don't think it is something that has to do with having two sound cards, since I have only one. By using a USB headset it like having a second sound card..seems strange but is like that, in fact in your sound settings (computer and ts) it let you choose between both sound card and headset.
Hope is clear enough
edit: here's the headset i'm using.
http://www.amazon.co.uk/Logitech-He...1HTI/ref=sr_1_1?ie=UTF8&qid=1248903325&sr=8-1
I have to say it's not the most confortable but couldn't afford more.