Just install it without putting in the License Key nor activating it. When you have finished installing it, install it again over the installation you just did, this time putting in the License Key and activating it.
Only Mac Pros and MacBook Pros manufactured in 2008 include Boot Camp drivers 64-bit Windows. All other Macs include Boot Camp drivers only for 32-bit Vista. You can download the 64-bit Vista Boot Camp drivers that will work with other Macs from the web, but you need to search for them.
Unless you have 4GB of RAM, you won't really notice any difference between 32-bit and 64-bit Vista (and even then...).