Found the solution:
Open up a guiminer and click elsewhere to lose focus
In the taskbar, left-click once on the Guiminer icon so it gains focus
Now, press "ALT-Space" (you will see a menu appear were guiminer should be)
Press "M" to choose the Move option (your cursor will now turn into four arrow points).
Press any of the cursor keys once (this will move your guimineron the screen and it will be captured by the mouse)
Move your mouse about and you will see the guiminer moving with it
Left-Click to "drop" guiminer onto your desktop