There is a way to upgrade Windows Vista Enterprise to Ultimate (not enabled by default)
Before inserting the Windows Vista Ultimate CD
Go to, Start, Run: and type: regedit.exe
Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion
Change the key : ProductName from "Windows Vista ™ Enterprise” to “Windows Vista ™ Business”
Change the key: EditionID from "Enterprise" to “Business”

Do not restart

Now insert Windows Vista Ultimate CD and start upgrading (the option Upgrade will not be graded out anymore)

Gil D.

I'm a bit confused.... In the title you say one can convert it from Enterprise to Ultimate yet in the post you are talking about Enterprise to Business! Slip? Also, the key you installed it with won't let you transform it (and I'm sure this falls under the incidence of rule #1 of msfn...). Although interesting, I believe you should read the rules before posting. Cheers.

No, its not strictly violating rules.
His method explains how to make vista-setup think its a Business Edition & hence allows you to upgrade to ultimate.

Nice tweak, wondering if it breaks the EULA though?

LOL Dang near everything breaks the EULA!

Now thats worth quoting!

wow nice, does this keep using the VLM activation key of Enterprise, or do you still need to use up one of your MSDN Ultimate activation keys? (you only get 10 Ultimates per MSDN) if not, what does this really get you in the end? I guess if you have a lot of stuff installed/tweaked it's a time saver.

This simply allows you to update Vista from one version to another. The keys are locked to the software so you wouldn't be able to use the same key. Just like I thought I would get over by getting the Student version of Vista home premium for $65 then pay the upgrade fee to Ultimate, it doesn't work. It knows I have an academic version and makes me pay the full price to upgrade to Ultimate.