Hey Haze, if you have Windows XP
OEM then im afraid you will have to purchase a new copy of Windows weather that be XP or Vista. Since the OEM versions of Windows is bound to the system that it is originally installed on and can not be transferred from one machine to another without violating the EULA.
If anyone is looking at purchasing a new system and needs an operating system then their is no reason not to go for Windows Vista. Windows Vista is a brilliant operating system. The Aero effect and User Interface (UI) is fantastic and is very nice compared to Windows XP in my opinion. The whole operating system is very fast and extremely reliable.
The support for Windows Vista is now excellent and the majority of the hardware and software out their now work absolutely fine under Windows Vista. However please take into account that Windows Vista 64-bit cannot run 16-bit coded applications and also some decidedly 32-bit applications actually have an inclusion of 16-bit code in the installers. However that's very far and few between and really isn't something you need to worry about unless you specifically know of anything that you use that is 16-bit encoded in any way.
You're also probably debating on which edition of Windows Vista to purchase.
Here is a great graph that compares all of the editions of Windows Vista with one another. The two you are most likely looking at are Windows Vista Home Premium and Ultimate. I have used both and in my opinion Vista Ultimate is not worth the extra £50 over Home Premium.
Now as for either going for the 32-bit or the 64-bit edition of Windows Vista, this all depends if you have a 64-bit processor. If you have a processor that is capable of handling 64-bit instructions then their is no reason to go for the 32-bit edition. You won't see a massive performance increase going from a 32-bit to a 64-bit operating system as of yet since many programs have been written for 32-bit architectures. However this will be changing in the future because with 64bit being more recognized, more and more programs will be written under 64-bit architectures. When programs are released that are written specifically for 64-bit, you will then start to see a performance increase from 32-bit applications.
