Technically yes, although depending on whether it's retail (purchased from a store or online) or OEM (shipped with the PC) will determine if you need to call Microsoft or not. However, in either case, yes you can.
System Manufacturer/Model Number HP Z400 workstation OS Windows Server 2008 R2 CPU Intel Xeon 3550 @3.06GHz Motherboard HP Memory 16GB DDR3 Graphics Card Nvidia Quadro 600 Sound Card Realtek ALC262 Monitor(s) Displays 2x Hanns-G HG281 Screen Resolution 1920x1200
Keyboard Microsoft Natural Ergonomic Keyboard 7000 Mouse Microsoft Intellimouse Explorer 3.0 PSU HP Case HP Hard Drives 1x Samsung 160GB SSD
2x WD 1TB (RAID1)
thanks for the fast reply.
I just want to make sure, so I can register x64 retail version on a computer that had x32 retail version registered.(of course I would format my main hard drive and install x64 version
System Manufacturer/Model Number HP Z400 workstation OS Windows Server 2008 R2 CPU Intel Xeon 3550 @3.06GHz Motherboard HP Memory 16GB DDR3 Graphics Card Nvidia Quadro 600 Sound Card Realtek ALC262 Monitor(s) Displays 2x Hanns-G HG281 Screen Resolution 1920x1200
Keyboard Microsoft Natural Ergonomic Keyboard 7000 Mouse Microsoft Intellimouse Explorer 3.0 PSU HP Case HP Hard Drives 1x Samsung 160GB SSD
2x WD 1TB (RAID1)
If you do decide at a later time to clean install from 32-bit to 64-bit, here's a lot of useful information that may prove useful in these tutorials linked below.