Trying to attach an older version MSDE

I created a local development database and had tables that I imported thru Enterprise Manager. It was version 2000 (I think). I installed express 2005 and did a "previously registered servers" thing and it won't connect stating that

TITLE: Microsoft SQL Server Management Studio Express
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Attach database failed for Server 'ITPETELXP\SQLEXPRESS'. (Microsoft.SqlServer.Express.Smo)

For help, click: http://go.microsoft.com/fwlink ProdName=Microsoft+SQL+Server&ProdVer=9.00.1399.00&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.FailedOperationExceptionText&EvtID=Attach+database+Server&LinkId=20476

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ADDITIONAL INFORMATION:

An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.Express.ConnectionInfo)

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Database 'viperTSQL' cannot be upgraded because it is read-only or has read-only files. Make the database or files writeable, and rerun recovery. (Microsoft SQL Server, Error: 3415)

For help, click: http://go.microsoft.com/fwlink ProdName=Microsoft+SQL+Server&ProdVer=09.00.1399&EvtSrc=MSSQLServer&EvtID=3415&LinkId=20476

But when I look, it's not read-only.. what gives