What kind of scenery textures? For scenery objects that's no problem at all. For other types of scenery (i.e. terrain, landclass) you would have to try it and see. Some would require mipmaps as well.
The difference between the two is that the DXT3 image is compressed, while the 32 bit texture is not. Think of a 32 bit texture as a regular 24 bit BMP texture with an 8 bit alpha channel added to it. The 24 bit BMP is the "standard" BMP file as used by most paint programs, using "millions of colors".
If you use a lot of 32 bit textures in a scene you will fill your video card memory rather rapidly; they are 4 times the size of a DXT texture.
I want to use 32 bit textures for objects like buildings! Thanks for your explanation, but when you say that if i use more 32 bit textures i fill my video card memory which is the result? Could fs2004 crash?