Wireshark is great. I use it for part of my CCNA course as it gives so much information.
One thing you should know though, it wont monitor ALL network traffic, it can only monitor unicast, multicast or broadcast traffic that reaches your machine. If PC A send a file to PC B, PC C (your pc) wont detect the transfer on wireshark.
The only way to get wireshark to detect everything thats sent is to have a PC act as a switch/router, where by all traffic has to go through it. Or use hubs instead of switches, but i dont recomend that.