I'm just curious as to why you would need to switch to the old one. I've tinkered with a cheapo tablet that required the old google market and some fancy timing to gain root access, but don't know of anything on the prevail.
If you're having the issue where google play won't show you your purchased apps, it seems to work better if you go through the setup and log in, let it update all the way to the regular store homepage, then reboot the phone.