You dont need both to install.

I use VNC to view my Vista platform on my n800 and all I did was point the Application manager to the .deb file click here and the installtion will begin.

OR you can just go on the maemo website and click the .deb file and it will automatically download and then ask you to install.

Check out my short video of my n800 with VNC.

BTW: If you use an ADSL router which is behind a firewall make sure you go into your configuration ie: http://192.168.2.1 and open port 5900, as vnc works through this port and also set to which IP address it will be using for example on my laptop my ip address ends in 2 and my n800 is usually 3 so I set my n800 ip address to open port 5900 which will then connect to my laptops IP thus making a server connection.

Sorry if this isn't clear that's basically what I had to go through before hours of fiddling about. also the cool thing about VNC is you can rotate the screen so you can view it like a PDA (vertical).