At bando's request- I've written a quick tutorial that explains how to obtain the pokes for a trainer that allows you to join as VC in coop.
1) Join a CTF type game (or similiar) as either team
2) Search for 4 byte unknown
3) Change to opposite team
4) Search for value has changed
5) Repeat Steps 3-4 until you've limited down the values to a few
6) Enable auto-hack
7) Set hardware (H/W) write breakpoint on first address
Change team (H/W write breakpoint will fire)
9) Nop out the instruction that popped up in the lower window
10) Change team
11) If the nopped out instruction still allows you to change team (must wait till after respawn to check this), Undo the nop- and repeat steps 7 - 11 until it doesn't.
12) Take note of the address of this instruction and the poke code(s) (should be 0x90 for an x86 NOP [No-operation]).
13) Take note of the values you obtained in step 5 for the each team (0 for US, 1 for VC as far as I remember).
Now you can build your trainer- simply poke the value you obtained for VC into the address you found during step 5; and apply the nop pokes to the cancel the update team instruction to prevent over-writing.
Thats it!
Subsky