OEM vs Upgrade versions of Vista

Hey guys Great site and its helped me loads before, I'm sorry my first post is a question but this seamed the best place to ask for reassurance.

Im upgrading my rig before going to university and finally wanted to take the leap from 32 bit windows to 64 bit. I have decided for various reasons to stick with windows vista over moving to 7 or waiting for 8. I have i identified several options available to me, the main limiting factor being availability however i have a few questions regarding them. Either i purchase an 64bit OEM copy of home premium or I purchase a Vista Ultimate upgrade edition (with both 32 and 64 bit disks).

I know how the OEM version will work (it is effectively the 64 bit version of what i am using now and have experience with) But i am a bit rusty as to how the Upgrade Disks work.

Is it possible, using an upgrade disk, to upgrade from windows vista 32 bit Home Premium to 64 bit Ultimate?

I have heard rumors that the "OEM system builders" cd keys can be used to install 64 bit or 32 bit versions of the software without issue assuming the corresponding 64 or 32 bit disk is used. I this true?
(This is more for reference as i intend to put the old board and cpu to good use in the near future. The system upgrade of my main machine is going to be so substantial that im practically building a new pc which would breach the terms of use.)

Can you tell me any other pros or cons i will face by using the OEM version or and upgrade version?

Thanks
-Revodb

Whatever you do, moving from 32-bit to 64-bit will require a reformat - so back up to external media first!!!

You do NOT need to purchase anything - your current Key is valid for both 32-bit and 64-bit Vista.

What you will need is the 64-bit installation media - you can download a set of files for it from the links on these pages...
http://www.heidoc.net/joomla/technology-science/microsoft
The links are for downloads from the Digital River server run for MS.

You will then need to create the bootable DVD from those files -

To create the disk, see this set of instructions from Andre daCosta Repair man removed Windows Vista and installed Windows 7. How to I get - Microsoft Answers

Then you're all set - so long as you have the proper Product Keys for all your software (including Vista, of course) recorded offline somewhere.
Make sure that you have the essential system drivers downloaded and backed up so you can install them before connecting back to the internet, etc.

Welcome
If you follow the steps in this tutorial you will have the greatest chance of success. As Noel has mentioned back up your stuff. I would use Macrium to back up the entire OS, too, just in case there is a need to go back.
http://www.vistax64.com/tutorials/68767-clean-install-upgrade-vista.html?ltr=C
Macrium Reflect FREE Edition - Information and download