Your problem is that Gimp is for 2D art, while meshes are 3D. With gimp you can edit textures or make new ones, but can't do anything to the actual models (meshs). You need a 3D modelling program to edit meshes, like XSI or 3ds max. However, you need 3ds max to open the Sins meshes, as XSI can't use .mesh format. You then need to use 3ds max to convert it into something readable by XSI, and then you can use XSI to turn the model into something Sins can use.

And 3ds max is not cheap. I believe that the base version is ~$300 (but don't quote me on that). XSI is free, so you can create your own, new models, but you can't edit existing ones.

You're not totally out of luck. As I said, XSI is free, so you can create your own models. Also, some people have converted the Sins models into formats that XSI can read. If you want, I can give you the link to the converted capital ships from the 7 Deadly Sins forums.

It turns out one my buds who's into games actually has 3ds max, I'm probably just going to borrow his copy of it.  Thanks for all the info though it really helped me out