Linux Web Monitor Tool Recommendation

I'm setting up a small office network and I've setup Ubuntu server 10.10 maverick meerkat. The system is going to serve up a few intranet pages so I figure it could monitor web traffic for them too. The company has a firewall and a managed switch. My first idea was to port mirror the uplink on the switch to the Ubuntu port and load some type of monitor software. Their building setup really doesn't allow me to place anything inline with the router/firewall using two network cards.

I've gone through several lists of bandwidth monitoring programs for linux, but I need something simpler that just tracks internet usage in a readable format. I only need the site visited and maybe the time on site. Any suggestions.

Ok, I just port mirrored my switches uplink port to a port with a machine running XP and Capsa software from Colasoft. The free edition looks like it's going to do exactly what I need.

My last problem is wireless packets being captured. Can routers send packets captured from users on wifi to the span port?