SCALE OBJECT TEXTURE is what you want.
Default mode for texturing is to stretch your image so it covers each face. SCALE OBJECT TEXTURE allows you to tile the texture across each face by however many times you want. So if you had a long wall for instance that was 100 units by 40 units high, you may wish to tile the texture 5 by 2 so everything is nicely ratioed, so just SCALE OBJECT objnum,5,2 - simple as that. Beware though that is applies that tiling to every face, so for cubes and boxes made to look like walls, the thin edges of the walls will look squashed.
Boo!