I'm pretty newb myself, but if I understand you... you are refering to gaining a command shell on remote computer correct? Or are you looking for a graphical UI view of their desktop? Or... from your question are you asking how to connect to a computer that is networked to a computer that you know the ip of, but are unsure of the target box?
Either way, there are a ton of both proprietary, and simple methods for both. You can ssh or telnet into them if you have user names/passwords and you just want a shell interface, which will allow you to look around the drive, execute code, etc. If you're after something akin to a more graphical look, you can use something like PCanywhere, Dameware or even remote desktop. Thing is with those, they generally require prior setup on the box to be connected to, or confirmation box-side by someone there. Good tools for helpdesk techs etc. With the SSH/Telnet you will need open ports that are generally not open.
Assuming that this is an ethical entrance, and you own or administer the boxes setting something up like this should be no problem. If you are looking to break into the boxes, and have no permission to do so finding further answers would more likely than not require a different site. There are a number of ways to open a shell on a remote computer through OS/app flaws, and there is a lot of documentation for how throughout this site. I hope I answered some basics for you, and that I understood what you ment correctly.
Also, for port status discovery, OS fingerprinting, and generally great info on a target machine, Nmap is indespensible.
Last edited by g00d_4sh
on Fri Nov 09, 2007 1:53 pm, edited 1 time in total.
"Bad.. Good? I'm the guy with the gun"