Network simulator?

do you mean something like Hamachi?

hamachi is remote access (logmein). but I mean something like virtual environment – you can drag computers, add switches, routers, cables, then connect computers, configure LANs, that’s for training, you can see how all that stuff is working

I think you mean packet tracker.
Image: http://i270.photobucket.com/albums/jj87/photopoint2/PacketTracker411.jpg

something similar…

If you want an expensive but buggy simulator, try boson netsim. You can also but bundled lessons and labs to play with.
My favorite free simulator is GNS3. You will need access to cisco router IOS software, but GNS is the best simulator I have seen. GNS is the best because it only emulates the hardware, and will run directly off the Cisco provided IOS. The hard part is getting you hands on the actual IOS.

Dynagen.org
This is the Cisco simulator website for download. Hope this helps.

Maybe they are helpful: CertExams.com CCNA Network Simulator, Network Simulator with Designer, Hopfield Network Simulator, Network Crash Simulator, SigmaPi Neural Network Simulator .