There is no vanilla models/textures etc. in the selection menus, so i cannot make new objects.
I only see files from the mods i have downloaded, do i have to exctract the files from the file archives or something?

'Selection menu?'
What do you mean?

If you mean stored on your hard drive, then yes, you have to extract them from the BSA files. There are utilities that do that for you. I happen to use "FO3Archive Utility" but I think FOMM will do it too.

http://i37.tinypic.com/npqbuw.png of what i mean.

That is exactly what WillieSea refered to. As GECK use Windows Explorer when you want to change a file, it cannot find files in BSA archives. So, you need to extract the files from the respective archives using a BSA extractor, such as FO3Archive Utility. FOMM also come with a bsa extractor/creator - look under Tools->BSA unpacker.

I recommend only extracting as needed, because it saves space (even if the files are uncompressed in the .bsa files, I don't think you can remove them without the game complaining, and I think they're compressed as well). With Fallout Mod Manager you can even do a search for the file you're looking for to find it much easier in the archive, and this works for Oblivion .BSA files just as much as Fallout 3 (and presumably Morrowind) BSA archives. Which reminds me, I need to check for an updated OBMM, I haven't updated it in months, if not over a year.

I tried to unpack a BSA before i posted the previous reply, but it gave me an error saying something about invalid directory, so i thought it was wrong
but now i realised that i have to put it in the meshes folder >.>

Thanks for the help