The easiest way is to exploit VS 2008's "online" feature. Basically you want to set your solution offline, then bring it online while connected to the proper Codeplex server. TFS should figure out the rest.
I don't think there is an easy fix... What I've done in the past is back up those files that I have edited, then do a "Get Latest Version..." for the files I edited. This should change the files back to being read-only etc... Now, check out the files the regular way and paste the backups you had into the checked out files. Obviously this really only works when there are a couple of files you have edited.
To compare local and server folders, you can check out TFS Power Tool. After installing it, you can bring up the source control explorer, right click on the server folder and then select 'Compare'. Folder difference window will display the differences. You can also right click on the differences to see available commands such as 'Get Latest' to update your local folder for example. Check out Bryan Harry's blog post on the power tool