Error in Creating and attaching a database in sql server 2005

Hi Sir...

I Installed sql server 2005 in my system(windows 7)

After installation..i need to attach database file in that server but i a getting a error message like this

TITLE: Microsoft SQL Server Management Studio Express

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"Failed to retrieve data for this request. (Microsoft.SqlServer.Express.SmoEnum)"
For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&LinkId=20476
The server principal "WELCOME-PC\WELCOME" is not able to access the database "model" under the current security context. (Microsoft SQL Server, Error: 916)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=09.00.1399&EvtSrc=MSSQLServer&EvtID=916&LinkId=20476

And also, if am creating a database means am getting a error message like this

CREATE DATABASE permission denied in database 'master'.

So What is the solution for this...........?

BaluJagua