No worries... just that a quick search can avoid waiting for an answer... I did answer where I knew... and only suggested a way to get an answer for the other part. Anyway, no hard feelings.
Usually, if something works in another distro it will work in Mint... maybe some extra work will be needed... but Ubuntu has very good hardware compatibility. If something works in Ubuntu, it is almost certain that it will work in Mint... because Mint is based on Ubuntu.
If you install the 32 bit version and want to change to the 64bit version, you will have to do a full reinstallation. Everything in your root (/) partition will be lost. Data in other partitions will be preserved... unless you format them
I would recommend installing the Mint 6 64bit version because it is stable... There are still some issues with the Mint 7 RC. This will avoid any problems you might have. Then, when Mint 7 64 bit is released, you can upgrade to that. But like I said, it is up to you.
As for your graphics card under 64 bit, either search for other users' experience with it in Ubuntu or Mint... or wait for someone who knows to answer.
Just remember, Google is your friend... most problems have been faced before... and a quick search will usually get you an answer.