They have to gain access to your comp in order to access your files. But with a sniffer program, they can collect copies of the packets being sent to and from your computer and put them together to look at what you have been looking at or read your IM's that is why you should use encrytion when posibble. is that what you are looking for? Onceagain though you can find this info in numerous places, it is not hard to find.
Another thing to consider if you are worrying about monitoring is that if you are on a comp that does not connect directly to the internet but throughh the LAN then the IP that the internet sees is most likely not your comps IP but the IP of the gateway. (Someone Correct me here if I am doing a lousy job of explaining this or am just plain wrong)
Also you mentioned something about changing your password. Most comps that connect directly to the internet do not have static IPs, they are "leased" to that comp from anywhere from one session to 1 week.
Now that being said changing your password will not change your IP and if someone is that determined to screw with you (which I doubt) then changing a password won't protect your account anyway. Passwords are the weakest form of protection IMHO. If a strong password was all that was needed to keep people out of a system then there would be no need for network security specialists.
One more thing if anyone was monitoring your comp usage from inside the network, I have a strong feeling your admin would know.
D, world destruction
Over and overture
N, do I need
Apostrophe T, need this torture?-They Might Be Giants