silicone base heat paste will work in a pinch, it doesnt have as good of heat transfer charateristics as AS5, but there is nothing saying that you shouldnt use it other than you will want the best performance possible to prolong the life of you console as long as possible.
AS5 has 88% metal oxides and silver in it which is what does the heat transfer. The silicone based stuff is more of a general purpose heat transfer paste, and wasnt nessecarily designed to do this type of heat sinking. It worked just fine in the old days where processors werent producing as much heat.(the white paste you see on older electronix)
You dont have to use AS5 either, there are newer types heatsink paste available that are just as good if not better:
tunic tx2
Silver Compound from Antec
Dynex at best buy
Arctic Cooling MX-2 (supposedly the best)
I did read that AS5 is available at most Radio Shacks so convienence isnt a factor in the US. Any way you go it will probably cost you $5-10 for the better performance.
Personally I would recommend staying away from the silicone stuff and getting something that was intended for your application. However on the other hand silicone thermal paste is like a million times better than nothing or the old stuff.
stay away from using toothpaste, i hear that stuff has a nasty tendency to catch fire
