Okay, if your at home on Wifi, go onto your PC type in google ''realvnc'' or tightvnc proceed with the install, its pretty straight forward, once installed, go to start menu, programs, search for realvnc or what ever you installed. Now click on realvnc server, this should bring it up down the bottom right task manager where your volume is and stuff, now (if on wifi) now bring on the windows command prompt (cmd) type in ipconfig/all now u need to find your local IP ipv4 it should be on that. it will be somthing like 192.168.0.1 (Preferred) next to it. This will be the ip you will type into your n900 where you asked. If your out of home you will see need your External IP which u can get from www.whatismyip.com

Hope that helps in some way