well if its two windows pcs u can just use remote desktop connection that comes with windows......if u need to connect to say a mac then use this http://www.tightvnc.com/download.php just make sure u have permission to be on the oter computer.
or utravnc (my fav)..there r many versions.
u will need to first run vnc as a service on the target computer and config it as share session for spying purpose. not that i've done it, but thats what i heard..lol
some good remote access software i've used: (pls feel free to add others u have use)
vnc
rdp
teamviewer
gotoassit
There not made to spy, i mean yes thats what alot of people do there really made for system admins that want to remotly fix or do something on a pc. There very easy to use but u need to be on the pc and set it to allow remote connection and then u need to know its ip.
If your running two windows pc's enable remote desktop connection on bolth of them then you should be able to connect use google itll show u how to use remote desktop connection its the easiest way then try messing with other programs
as for my question before..the machine would have to be powered on to view it correct? Or would you be able to access it turned off? Like for example if my home computer is off can I access it from my laptop? Since I would be able to obviously give myself permission to view my desktop,If I needed to see a file etc? I would think I could send files in that manner also?