Screen capture is a fairly tricky thing courtesy of overlays (used largely for video and games) and that is where many programs fall over.
If you mean dial in an have a look at the screen then you want a VNC program (remote desktop is also a term but VNC will probably net you a better program). There are any number that have varying features (free, not free, need for a known IP, no need for a known IP, NAT traversal, OS agnostic or windows to windows only, need for you to open a port and so on and so on).
It is probably not so good for covert monitoring but teamviewer has a portable version.
I used one called Camtasia Studio, that worked really well and had great quality. You'll need to look for a cracked version though, unless you want to pay for it.