Does packet tracer show anything? What did you add to the routing table? Is there a router it's forwarding to? Could you post the config (minus passwords and external IPs)
MrGuvernment,
It's pretty easy to only allow your DHCP address range through the router. Assuming your usable internal address range is 10.0.0.1-10.0.0.254, here's how you do it
login to the router then type:
ena
config t
access-list 102 permit ip 10.0.0.0 0.0.0.255 any
int fa0...
If they're all coming from the same source, I'd just modify your ACL to drop that IP address once it hits your router. I tried Googling for that IPS signature but it didn't really turn up much.