The Debian packaging for Wine is now stored in a Git repository on alioth.
$ sudo apt-get install git-buildpackage pristine-tar
$ git clone git://git.debian.org/git/pkg-wine/wine.git
If you need it, information about actually using Git can be found in the Git User's Manual.
But here's a tip: to update your local copy of the Debian packaging, you can do:
$ git pull
$ debian/maint/build
This should invoke git-buildpackage with the appropriate options.
$ debian/maint/build-final
This will invoke git-dch to generate a changelog file and open it up in an editor for you to prettify (you almost certainly need to). Once you exit the editor, the changelog is committed, and git-buildpackage is invoked to build the final packages and tag the Git tree. You could then upload the result.
You could run uscan. But if you feel like doing things manually, first download the .tar.bz2 from WineHQ, then do
$ debian/maint/import --upstream-version <version>
<filename>
If there are no merge conflicts, you're done. But if there are, you need to resolve them. It's probably cleanest to use the deb/* branches for this purpose (at least if you plan to push the result to git.debian.org later), though not necessarily easiest. Once the conflicts are resolved and the result committed, complete the import with
$ debian/maint/import-done --upstream-version
<version>
(Note that this will replace the commit message of the merge you just did with some information from upstream's release announcement.)
Of course, follow up by building the package as described above.
If you're interested in contributing to the Debian Wine packages, you should subscribe to the pkg-wine-party mailing list.