Cheers for the advice everyone. To be honest I played about with hammer for about 3 or 4 hours and got a tad overwhelmed. I think my ideas are way out of the scope of my abilitys!
Managed to get an ultra basic map compiled, flat ground and a few models with lighting and textures. Looked absolute guff but I'm getting the basics.
One important thing though, I didn't really enjoy doing it. It'll be weeks if not months before I'm competent enough at this to make something that I want to make and I'm doubtful I'll remain interested for that long. Think I'll still plod away at it for a while (I'm doing a Computing Science degree so it's prob gd experience anyway) but I'm pretty sure I won't make a functioning DODS map for a long time!
Unless... I just make a big box and spawn both teams right in the middle, that'd be fun for a while