Right click on .LDF and .MDF files and uncheck read-only attribute.

>an error ocurred when use 'Attach Databases' option that i downloaded form a site which sold a book to me, those are northwind and pubs from sql 2000, the error message were the following
>Attach database failed for server 'nombreequipo1'
>Additional information
>An exception ocurred while executing a Transact SQL statement or batch
>DAtabse 'Northwind' can not be upgraded because it is read only or has read only files.Make the database or files writeable, and rerun recovery.
>
>My question is how can i make this database writeable or whta other thing i can do?
>