Hi,
I am thinking of upgrading to VISTA 64-Ultimate edition.

I currently run Home Premium 32 (full copy).

Do I need to order the Ultimate 64 OEM Edition only?

If I upgrade from Vista Home Premium 32 to the Ultimate 64 Vista edition will I need to reinstall all of my applications again? (including photos etc)?

You cannot upgrade. The kernel (core) of Vista 64 is completely different from the 32 bit version, so you must do a clean install. The same applies to XP32 versus XP64.

Back up all your stuff, and be ready to reinstall everything - So don't forget to print copies of all your licence keys. If you trust Microsoft, you can install to the same drive/partition. Vista will detect the older installation and create a folder called WINDOWS_OLD which will contain all of your old data. Be advised that there is the likelihood that any DRM-tagged content may be deactivated. So if your service allows it, back up all of your music online and re-download it directly to the new OS.

If that sounds as painful to you as it does to me, then another solution would be to buy a second hard drive, unplug the old HDD, and install Vista 64 to the new. When all is done, plug the old HDD back in. V64 will see it and will be able to read your data. No dodging reinstalling your programs tho.