Here are a few links I found a while ago that might have some info for you.
http://www.drugtext.org/sub/marmyt1.html; This one states you would have to literally have to smoke 40,000 times more pot than you would need to get stoned to OD on marijuana.
This link states,again, it is virtually impossible to OD on pot.Marijuana
Even Wikipedia says its impossible.
These misconceptions about pot are really a bummer! It gives pot a bad name, and its not so bad
For good measure here is another one that states its impossible-http://www.mpp.org/site/c.glKZLeMQIsG/b.1146183/k.AE54/FAQ.htm

Even erowid says:"Nobody has ever overdosed. For any given substance, there are bound to be some people who have allergic reactions. With marijuana this is extremely rare, but it could happen with anything from apples to pop-tarts. Not one death has ever been directly linked to marijuana itself. In contrast, many legal drugs cause hundreds to hundreds of thousands of deaths per year, foremost among them are alcohol, nicotine, valium, aspirin, and caffiene. The biggest danger with marijuana is that it is illegal, and someone may mix it with another drug like PCP.

Marijuana is so safe that it would be almost impossible to overdose on it. Doctors determine how safe a drug is by measuring how much it takes to kill a person (they call this the LD50) and comparing it to the amount of the drug which is usually taken (ED50). This makes marijuana hundreds of times safer than alcohol, tobacco, or caffiene. According to a DEA Judge ``marijuana is the safest therapeutically active substance known to mankind.''
So there! Put that in your pipe and smoke it!:smokebong: