What are you trying to do precisely? Your iMac IS on the network, otherwise it could not get to the Internet via that network. Do you want to make files on it available to the PCs? Or share printers attached to it? Use printers attached to the PCs? Access files on the PCs?
What operating system(s) are the PCs running?
Let us know, we'll keep helping you.
Best of luck.
thank you very very much.
this problem (add Mac to existing home network, enable to read and write into PC on network)
has bother me for months, waste me numerous hours. when I following the instruction of your article,
I found out the actual problem is Window7 did not share the C: drive itself (even I shared fold under C: drive).
you solve my question, you are great.