I understand what you're saying. But chances are if you purchase an updated installation DVD, will will only get exactly what your PC came installed with and that's it. You might have the latest service pack, but you'll still be getting a 32 bit version of your OS.
Your alternatives are to become a MSDN tech net subscriber and download the OEM version of Windows Vista Home Premium and see if that works. Or you can check ebay to see if someone is selling a Vista x64 recovery DVD for your OEM.
I don't know what your saying, or you don't know what I'm saying.
My PC didn't come with anything. I built it. From scratch, with individual parts. I got the case, MOBO, CPU, GPU, RAM, HDD etc all separate and purchased a Vista DVD (in a box and case with a manual COA and product key) to install vista on the HDD I bought and installed in the computer I built. Now I would like to get a few new parts and upgrade past 4GB RAM. This is still the same computer with the same MOBO and CPU (currently, may upgrade).
The version of vista I bought at the time came with only a 32bit DVD and no service packs (as far as I can tell). According to MS if you purchase a copy of vista yourself to install on a PC you built yourself then you can use the product key you got with either a 32bit DVD or a 64bit DVD. I don't have a 64bit DVD but would like to get one or download an ISO so I can make one. If I can get the ISO with the service packs included that would be nice.
There is no recovery disk, and I am the "OEM".
If you want to know, I built this computer with:
Antec 300 case and 620w Neo Eco PSU
Gigabyte MA790GPT-UD3H MOBO
AMD Phenom II X3 720 CPU
4GB (2x2GB) DDR3 1066
ATI Radeon HD 4850 512MB
Seagate 320GB 7200RPM SATA HDD
CD/DVD Burner
Vista Home Premium 32bit
Now the computer is being upgraded:
Same Antec case/PSU
Same MOBO
Same CPU (may upgrade to X6)
Potentially 8GB (2x4GB 1600 or 4x2GB 1066)
AMD/ATI HD 6950 2GB
Potentially 1TB Seagate 7200RPM SATA HDD (not sure if it works)
Same CD/DVD Burner
Same OS and key, but 64bit instead.