Today, I ask my friend, working at Microsoft Thailand, about license. My mind is changed a little bit.
He told me that I didn't need to buy separate license for x86/x64. The license I should buy is x64 because it is downgradeable (to x86/XP). If my university gives me MSDNAA license, I will get Vista x64 + Office 2007 license for free. (WOW!)
Actually, it is a politics. Sales have their politics so their answer may be not accurate.
In Commart XGen 2008, there are cheap Windows Licenses for sale. The licenses consist of: Windows Vista Starter, Windows Vista Home Basic, Windows Vista Home Premium, Windows XP Professional/Windows Vista Business, Windows Vista Ultimate, and Office 2007 Home & Student.
I am really interested in Windows Vista Ultimate license (even I used to have it license). So I ask dealer with simple question, if I want to reinstall Vista Ultimate x64 on x86 on the same machine but not now which license should I buy. Can you guess what is an answer?