Well thank you guys for all your help, but I got my map using that big image tutorial I found.
See, the issue was I didn't want to create a whole new map. After following the tutorial on the Steam forums, I quickly figured out that thats what I was doing. So I stopped.
I wanted to get an image of the pre-existing map that was created by Valve, so I knew where to apply texturing for <insert part here> of the model itself. And I got it.
I also sent it off to a friend of mine who runs a TF2 server, and who needed the sheet, as a plugin he's making is going to use the Nail Grenade.
However, I haven't actually tried my hand at texturing the Grenade using the above sheet, so I'm not sure if I moved the UV map into the box (as per the image tutorial) properly.
Guess I'll find out when I actually try texturing it. And hey, with that method I found, I can nab texture sheets for all the other scrapped grenades in TF2.
Again, thank you all for the help, I'll keep you guys in mind if I need any more help with 3DS Max 9.