Can you see other computers on the Cable broadband ...

As far as I know, the Cables company makes sure that you won't be able to access any other IP that belongs to their internal networks other than the various servers needed to gain access to the Internet. They are blocking access to other IP addresses similar to the one you get when you hook your computer to the Cables modem.

I don't think it's possible through your ISP's servers legally, as Muffler said. You can always try to scan ports on various computers within the IP range of you ISP. Scanners like Angry IP Scanner would be sufficient. Plus, using this particular scanner you can scan ranges and determine whether they are online or not. If that's what you want.

You can find Angry IP Scanner by using Google. :)