Not yet, Seannewboy. They are planning on enabling that feature later so that the F2P system can be tested in it's entirety. But for now, current subs are still subs to test the Cartel store. Unless, of course, they've done something and I missed it as has happened in the past. :(
Jacien, you shouldn't have to choose anything. When you log into PTS using your current subscriber login credentials, you should be directly in-game on the PTS server. When you opened the login screen for the game, you have to click on the icon directly across from "exit" to get the box to enable PTS. Did you do that before "downloading"? If so, after downloading the PTS client, you have to open the login screen again and will probably have to click on that same icon again to enable PTS login. You then use your regular login credentials to login to PTS and play. You will have to create characters to use on PTS as they didn't allow for copying existing live characters to the PTS server for this test. Maybe that's the problem, you don't have any characters to test anything with so nothing is looking or working as it should. Let me know what you've done so far and I will try to help you get on PTS to try stuff out. :)