http://www.cisco.com/en/US/tech/tk64...800e523b.shtml

Thats a pretty good comparison between NAT and PAT.

and btw...
f your router is doing a NAT:
a) all requests destined to the public address( scans/hacks/trusted..etc) always
get forwarded to your PC.
that depends on the setup of your NAT. A NAT can have 10,000 machines behind 1 NAT router and that router is not going to forward the packets to every machine behind the router. As a matter of fact, unless you specifically tell the router to send the packets on, the router will drop connections that are iniated from outside the network.