Building a Network Tap

I'm starting a new project on building a network tap. I was thinking of building a passive tap, but i need it to deliver without any network errors.

I'm going to try to build active network tap that is positioned between a router and modem. I need the tap to capture all the packets and dump them into the a file, which i can review later.

I'm going to use a laptop as the base for the system, and i was also going to add another lan card to it. I was also going to use the wireless card in the laptop to either connect to a network, or create an ad-hoc network where i can access the device using a remote administration tool.

Does anyone see any problems with this set up? or any suggestions?