Help is always welcome.
We do not have much documentation on how to get started with localization so I am not sure how familiar you are with localization in .NET. http://msdn.microsoft.com/en-us/library/ms247246
Basically the best thing to do is get the source (or create a fork preferably), copy all the resx files to new ones with the es-ES in the name and translate each string. There are some tools to help though, http://resxtranslatorbing.codeplex.com/
Also, someone has translated many of the strings before but in the old database localization format we were using before. This would probably give you a huge head start.
Certainly post back with anything you need though.