BetterTouchTool lets you do this: http://boastr.net/ (it's free and quite handy!)
In BTT's prefs, click on the "Action Settings (window stuff etc)" button.
Then select the "Window Moving and Resizing" tab.
The bottom pane will have 3 options, choose whichever you like:
I selected all three: move, resize, and FN.
When I hold FN+CTRL the focused window will move when I slide around on the trackpad.
When I hold FN+OPTION the focused window will resize when I slide around on the trackpad.
I tested this on my macbook pro, mac os x 10.6.5.
Note that you may get this message first time you try to actually move or resize a window:
Click "Launch it for me!", then check the box for "Enable access for assistive devices" - you're in business.