Unfortunately running Vista with 1gb is pushing it. Vista really needs to have at least 2gb to run decent. This is probably why you are experience such slowness. Even running Fluxbox or Xfce would be pushing it.
You mentioned that you cannot burn it to a CD; do you have a USB stick that is at least 1gb in size? If so, you may have the option of using Pendrive Linux
that will allow you to put Mint 6 onto a stick and boot from it this way. It's quite easy to do by following the instructions.
Then, if you want to, shrink your Vista partition and make room for Mint.