I want to make new textures but the GECK only uses DDS files, so I'm searching for a program that I can use for creating those DDS files. I've decided to use Paint.NET, but first, I need to know if it can save/open/edit DDS files. So that leads us to the question: Does it already come with those features without having to download addons?
This will help alot, thanks.

yes, though how good the compression quality is I cant say.

exactly the same as every other app will be... the dds compression algorithm(s) used will be identical no matter what you do it in.

now if you are talking about mipmap interpolation and filtering... that's a whole other story.

not true.

Why not? Is that not the point of a format? To give you consistant size compression, and readable format. If it compresses differently depending on what you use, that would be rediculous. So your saying a PNG could compress smaller in one program, then a JPEG could in another? If they dont compress the same, then one of them is not the true dds format.

S3TC algorithms are always the same. Or else they aren't S3TC algorithms, they are something else.

Pretty much what he said.

No, the .dds specification is the same, but the algorithms of getting input to output pixels differ. Try taking the same image through several dds compressors and comparing the results; something that has a wide selection of colors/borders and shapes. (dds doesn't handle small circles well as a whole.)

edit: Just saw this a bit ago, it's super-sixy:http://www.gamasutra.com/db_area/images/feature/3759/bc3_bc7.png

Thats awsome considering Fo3 uses BC3. -_-

Yes, but it's just an aside that I thought I'd share.

ah, I see.

If you are able to download programs I suggest using GIMP. Best free image editing software out there imo.

Needs a dds extention I think but that takes an extra minute/minute and a half to download and install. Well worth the time if making textures as it offers massive flexibility and is very forgiving if you make mistakes. (never used paint.net so I don't know if that's any better).