Is it possible to convert an Microsoft SQL 7 database into Microsoft SQL 2008?
Migrating a Database can include
depending on if you just need the data and its schema or you need everthing your options will be different
In any case from what I gather MS only supports skipping one version but not two. This means you'll need an intermediate step of upgrading to 2000 or 2005 before you can upgrade to 2008.
these guides will help you figure out what to do