Yes this is possible (You can also download models, sprites and maps from www.esf-world.com) Modelling:
There are various modelling programs, Maya, 3dstudio Max, Milkshape, Lightwave, just type them into google.com and see which one you like best Mapping:
If I'm right, the program for mapping is called Valve Hammer, just google it. Sprites:
You will need Sprite Wizard and Sprite viewer to create your own sprites...