Problems Installing Vista in 64-bit Mode

Hi everyone,

I apologize if this has been asked countless times before, but I am an XP user who just recently purchased a Vista Business upgrade disc which is being installed as a completely new installation on a new primary hdd partition on my computer. The problem I seem to be encountering is that during the installation process, I've never been presented with an option for choosing between installing a 32-bit mode or a 64-bit mode. I want to install it under a 64-bit mode because I use some more intense graphic editing and 3D modeling/animation programs and I'd like for Vista to see all 4 gigs that is currently in there. I read a few of the F.A.Q.s about installing Vista and I've already determined through the instructions presented in determining that my computer is able to support a 64-bit OS. It does indeed say:

64-bit Capability - Yes

So why am I not seeing any option to install Vista under this mode?

My computer specs are as follows:

Dell Dimension 5100
SATA HDD - 400 Gig - 250 gig being allocated to Vista Partition
4 GIG - OCZ DDR Ram... I believe it is DDR 3, but if not then it is DDR 2.
NVIDIA GeForce 8600 with 512 ram

Thanks for your help!

-Thomas

Ah, so after rechecking the package label that the student services sent to me, it says that it was an upgrade disc for Windows Vista Business - 32 Bit... So I'm under the assumption that the 64-bit was not contained at all on the disc which is a shame since the notion of upgrading to a 64-bit operating system was my entire reason for ordering this upgrade disc in the first place...

I noticed that for a time, Microsoft had a service/offer that would allow you to ask them to send you an alternate media kit disc that would contain a 64-bit version of the same version of Windows Vista that you had a product key for, which I provided on their website, only it could not find the offer anymore upon submitting my information...

What else would you all recommend I try? I feel like I'm running out of options and it is doubtful that I will be able to return this disc back to the academic reseller that I ordered it from, even if it is their own fault for not being more specific in their product description about the package only containing an upgrade license for the 32-bit.

Thanks for your time and any assistance with this would be much appreciated!

-Thomas