I would've put money aside for a new OS if I had that much RAM. I only have 4GB though, so I don't lose much with XP32. I do have a copy of Vista64 which I will be breaking into later for DX11...
Just a bit of FYI to understand the issues with 32-bit and 64-bit OS upgrades and later options that may or may not be available to you later:
When upgrading from Windows Vista to Windows 7 you must upgrade the version currently installed within Windows Vista to the corresponding version in Windows 7. I.E. Windows Vista Home Premium to Windows 7 Home Premium; Windows Vista Business to Windows 7 Professional; and Windows Vista Ultimate to Windows 7 Ultimate. You also cannot upgrade a 32-bit operating system to 64-bit -- to migrate from 32-bit to 64-bit will require a custom install.
Additionally, you will not be able to "upgrade" from a 32-bit version of Windows 7 to 64-bit -- the architecture between the two is too drastically different to allow such a change. To learn more about the differences between a 32-bit operating system and 64-bit please go to the following link: http://bit.ly/2aT3xP