You should be able to plug the TX unit (the receiver) via USB into your computer, pair the headsets with them and use them that way. Be sure to download the firmware updates first.
Just a word to the wise though. I bought a pair of refurbished A50's off eBay for $160 recently that I was going to use for my 360, but it wasn't outputting game audio and friends complained of a "tinny" effect to my voice. Sent it in for a replacement and while I had game audio, the "tinny" voice problem was still there with the replacement headset.
Long story short, I returned them and got my money back. I'd recommend you do the same and get a pair of Sennheiser 363D's. 7.1 headsets from a renowned company with almost audiophile quality. Astro's are just expensive Skull Candy's man. Once I found out Skull Candy owns them, I will have nothing else to do with Astro.