Analyzing… Searching for Something.

I am analyzing my NVIDIA nForce MCP Networking using the wireshark software (old Ethereal).
And Im looking for a specific protocol: DHCP
DHCP offer to be more specific.
I do reside in Brazil and i was informed that the service of broadband is sending packets to my modem with the purpose of controlling the speed and bloking most of the peer-to-peer services (such as Bittorrent, Napster and Gnutella).They deny all, and its not written on the contract.
So my question is:
When is the best time to Analyse and if can i focus my seach on UDP port (TCP off the seach).