Port Scanners:
These essentially are little programs that will test an IP ( or a range of IPs ) for open 'ports'. A port being a point where a system is open for communication. One of the best Port Scanners is 7th Spheres Port Scanner. I think you can find it in the archieves here. Or, its also in the archieves of Hackers.com.
If your'e looking for using the public proxy thingy, then Victor essentially expalined it pretty well.
Cheers!
