It's actually very simple and completely solves the problem. I've included a clickable thumbnail of a screenshot for each step, so here we go.
1. You need to open the gconfig editor by keying Alt-F2 and enter gconf-editor in the text box:

2. Next double-click on desktop to open the tree further:

3. Next double-click on gnome to open the tree further:

4. Click once on lockdown and you'll see selections in the right-hand window. Tick the disable_ lock_screen box, close gconf2 and you are done.







