Monitor ALL pc's (XP) via spy software?

[Chris Williams <realized () gmail com>]

I am looking for software that will let me monitor in REAL TIME, as
well as go back and see what happened on a pc at any time. I see quite
a few options out there and most seem to do the same thing which is
why I am writing this.

What do you guys recommend? I am looking for:

1) Something that can be deployed in the enterprise (40+ machines).
2) Able to connect from the network/LAN to monitor in REAL TIME - in a
way that is passive.
3) Able to go back and see what happened on the pc earlier in the day/week?
4) Able to monitor everything from one machine.
5) Option of logging urls they went to earlier etc.

What do you guys recommend?