It depends a lot on the design of the laptop and the design of the pad. The only way to know is to try. As a general rule though, the faster you can get the warm away and the cooler the surface you're putting it on the better. The problem with a lot of those cooling pads is that the material they are made of frequently absorb heat but don't disperse it.

First thing I would try, however, is cleaning it out. If you are not comfortable doing it, find a techie friend. Laptops, like desktops, can get clogged up with dust. The problem is that laptops need a lot less to cause a problem, and when it does build up, it causes more of a problem. The dust just acts like a layer of insulation in the whole thing. My suggestion, pop the battery, the hard drive, the CD ROM, anything that is is removable. Take off the keyboard (many laptops have lock switches on the bottom that let you pop the keyboard off without removing screws), and consider taking off the outer case. Once that's done, go through a six pack of compressed air.

As a side note, I tend to completely dismantle my laptops and removed the motherboards for cleaning every six months or so. Every time I do, I'm amazed at how much better that makes it perform.