Hauppauge just 'inofficially' released a new driver for all WinTV-cards for Windows NT 4 and 2000. The Readme isn't updated, so don't know what has been changed. For those who have troubles might try it anyways.

Get it here: ftp://ftp.hauppauge.com/hcws/Support/NTdrv308.exe

Greetings,
Kevin