Right, so deleting the Impulse folder located at "C:\Documents and Settings\All Users\Application Data\Stardock\" let me into Impulse. It recreated the folder and everything is working ok with Impulse now.
On the downside I updated Fences through Impulse and that did jack to fix the wallpaper issue.
Just to give a little more info, that I should have given in the first place sorry, I'm running what reports as Fences v 0.96.1533 Beta if I right click on the desktop and go to Edit Fences > About. It also reports as Fences 0.96.039 if I go and take a look at it in Impulse. My PC here is running Windows XP SP3 and I'm using UltraMon v 3.0.4 Beta with three monitors.
Last thing I'm going to try is just uninstalling Fences and then reinstalling through Impulse to see if that resolves the multi-monitor wallpapers problem that I'm having.