Hi Dion,
I used to run a CRT (replaced when it blew up
)on a 6600GT for a while and was more than happy with the results provided a never had to use the Windows desktop which was impossible to read and suffered from overscan. I never really noticed any overscan in the Media Centre and seem to remember using the zoom settings to make things right but the advantages of having a media centre in the lounge far outweighed any sort of issues.
Can you not just give it a go while the family's out - if they come back and it's all running then you're a legend. If it doesn't work then noone need know
Cheers,
Tak