NB - These screen shots will not match yours exactly, but they should be close enough.
1 - Find your Guild Wars icon - it's normally on your desktop, unless you've moved it elsewhere. If you've moved it elsewhere, I'm going to assume that you know how to open the folder it's in.
2 - Right click the icon and select [Copy]
3 - Right click beside the icon and select [Paste]
4 - Rename the new icon to something sensible rather than the default "Copy of..." - to do this, overtype the name. If you've already accepted the default, right-click it and select [Rename]
5 - Right-click the icon and select [Properties]
6 - Append [space]-image to the command line thus:
7 - Click [OK]
8 - When you don't need your machine for a few hours, launch the new icon.
NB - It seems to grab all the memory and all the CPU it can get its hands on, and it doesn't seem to want to "play nice" with other applications, so trying to use the machine for other things is a bit futile.