Remoter works fine on the iPad2, so that's not the issue.
Version 2.0 should be coming out soon with lots of enhancements, including better error messages. Until then, could you try connecting to your Windows machine from another computer on your network? Just to make sure your VNC server installation is working.
What version of ultravnc did you install? Remoter has been tested with version 1.0.8.2; make sure you're running this version.
Possible issues:
-Windows Firewall: try temporarily disabling it, just to see if this is the problem
-UltraVNC installation: please follow the steps from the video here:
http://www.youtube.com/watch?v=4z2xPX_pZ_k-IP address: If you're connecting while on your WiFi network at home, you need to specify the IP address of the windows machine.
You don't need to do anything with the router if you're connecting while on your WiFi network.
Hope this helps,
Raf.