Import from what mail program to Thunderbird? W7 comes w/no mail program at all, they suggest that you get their "live essentials" for mail, IM etc. that isn't included.
How do you start it? Manually? Try right clicking on the program, properties, compatibility tab and check run as administrator. Not sure if it will help but might be worth a shot.
Maybe there are left over bits that aren't being removed completely like norton crap does and causes problems. One of the other uninstallers may get rid of it. Then you can reinstall and see if it helps.
Please do Steve! With all of the misinformation out there I decided to not try the 64 bit since my vista was 32 bit even though I have a 64 bit processor. I wish I would've waited to activate because now I probably can't install the 64 bit and activate since I all ready activated my key as 32...