I started by looking at (and using, obviously) existing net tools, as separate programs
-7th Sphere Portscanner
-ms dos traceroute
ms dos ping
and so on...
Then i went into C++ builder and just designed the layout etc. put all the buttons and text boxes in the right place
put it in a page-control so that you get tabs labelled "Portscan" "Traceroute" etc.
Then I'm now working on filling in the actual code, by dissecting existing source code and putting in my own variants of it... only its taking a while cos this is the first internet,TCP/IP, sockets etc. programming I've ever done.
There's loads of Free Source Code websites out there, and my current task is browsing them all for the fastest and best lines of code...