I think this trainer has unlimited ammo for chris or sheva. I don't use trainers though, so I can't be certain.
http://z6.invisionfree.com/Resident_Evil_4_PC/index.php?showtopic=13366

I use those boards when I've modded RE4 and RE5 RE6. That is the best place I've found as the mods etc, police things quite well. I think it modifies the process, so it might make your antivirus go off no matter what.

I just take all the ammo away from sheva and let her use a stun stick, because the AI's aweful. Even then it's much more fun if you have anyone else that can play it with you.

Do not leave this running when playing a VAC enabled game. You will probably be banned.

Now there's a word I haven't heard in quite a long time.

Brings back memories of getting unlimited money, all research and happy guests in Roller Coaster Tycoon.