I've got the same problem with WinTV7 and a Hauppauge HVR900 HD USB stick. I have a good aerial and was receiving DVB-T via an Avermedia cardbus part on my old laptop. Unfortunately, my new laptop doesn't have a cardbus slot so a can't determine if it's Win 7x 64bit, the Hauppauge stick or the WinTV7 app causing the problem. I note that it runs OK on an analog signal, but freezes with DVB-T (both audio and video). I removed and re-installed the WinTV7 app and set up analog channels only. I couldn't receive analog after this, until I also set up DVB-T channels. Now I can get analog, but no digital reception (audio or video). If someone has this setup running under XP or Vista 32bit, I'd be interested to hear from them. I am of the opinion that much of this tuner USB stuff has pretty flakey software, with the vendors seemingly only interested in who can get to market first. Avermedia took over 12 months to get their software and drivers right, but their file format (MP4) is limited to 4G because they are using old 32bit SDK's. Not what I'm after. When I had the HVR900 working (sort of), I did a recording and it was nice to see a .TS file of some 12GB. So I'll stick with Hauppauge, use their forum, and pester them, until, hopefully a solution is forthcoming.
Hauppage have got an upgrade available (v1.3) for WinTV7, so you could try that, if you haven't already. It may be that the problem actually lies with Win7x64bit as I have a number of other apps that don't work properly, even though they supposedly have the 64bit drivers.