I had SQL2000 Dev Edition on my XP Pro. I installed SQL2005 on top of it. It installed without any problem. But @@version in 2005 Management Studio returns:

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Microsoft SQL Server  2000 - 8.00.760 (Intel X86) 
	Dec 17 2002 14:22:05 
	Copyright (c) 1988-2003 Microsoft Corporation
	Developer Edition on Windows NT 5.1 (Build 2600: Service Pack 2)


(1 row(s) affected)

What do I need to do to activate SQL2005?