Skinnable GUI in WinForms with C#.net

Well, you have quite a few options.  You can look into getting ahold of some prebuilt stuff that would give you a custom look (or at least a non-grey screen spec look); there are some free things and some that are not (look at steepvalley.net, Krypton 3.0, skincrafter.com, dundas, infragistics, etc.), or you can roll your own based on building your own custom controls used in conjunction with borderless transparent forms.