How to trac another computer in the same household?

first let me say I all for privacy but my son has his own computer in his room and his habits have changed lately. Nothing bad but constantly chatting on the computer in blogs, I think he has his own blog, chatting with older people, multiple email addresses, etc. What got me to wondering if he is hiding something is when I walk in his room he minimizes every IM, Chat, and WebPages. I try to discreetly look over his shoulder but you know teens they are aware. I was wondering if there is a way to view, in real time, his screen from my computer. I know at one place I worked I could go to view terminals and view each cash register [computer] as the employee was ringing up items. I kind of would like to know if something like that is possible with home networking. Again I don’t want to invade his privacy but at the same time I want to be a responsible parent. Here is the hardware I have if that makes a difference.
1.   Cable Internet in to cable modem
2.   From cable modem to D-Link – DI604 router
3.   From router – port 1 to my computer – port 2 to his XBOX, - port 3 to his computer – port 4 is Open.
4.   Both computers running Windows XP Home service pack 2
5.   I have not set up a network
6.   When I connected the router I did not have to do any setup except contact the cable company and give them the new Mac address.
7.   There is a set up in windows XP for networking and the software that came with the router has a network setup but I have not been able to understand how it works or if they will do what I’m looking for.

Any help would be appreciated.