The options to disable the hud and customize the crosshair are available in the game menus.
However, they don't let you disable your weapon. To hide your weapon for screenshots, you can bring down your console with Ctrl + ` (a.k.a ~, the button next to the number 1 key).
"r_draw_weapon 0" - hides weapon
"r_draw_weapon 1" - shows weapon
You can bind them in your My Documents/Shadow Warrior/profiles/profile (where profile is whatever you named your profile).
Open the binds.cfg file with a text editor and add the following lines:
bind +f3 "r_draw_weapon 0"
bind +f4 "r_draw_weapon 1"
Start the game and press the f3 button to disable the weapon, f4 to re-enable.