I only just found this thread. I am currently in Cambodia after being in vietnam for over three weeks. I'll answer as best I can. However, don't take my word as gospel as most of it is gained through reading travel books, talking to other travellers, my own experience and for some things I would be guessing. I'll ty and keep it in forum guidelines.
Drug Laws:
Both are very strict. Severe sentences are handed out, life imprisonment and death sentences are possible. Added to this the police of these countries are very brutal and operate above the law. If arrested being beaten in order to obtain confessions is a real possiblity. If charged your embassy cannoit get you out of trouble. The jails are supposed to be hell holes that make our jails look like 5 star resorts. In this sense there are many similarities with thailand.
The Police: In general they are corrupt. Cambodian police particularly. However, in order to get a bribe you have to have the money and the language skills to negotiate. The amount to be paid will depend on the officer and the drugs and their amounts. For a foreigner, it could easily be over $1000, if you don't have this kind of money and can't negotiate it down then your fucked! It is also entirely possible that will not accept a bribe.
There are less police blocks in these countries than in thailand which means travelling with drugs is a little less risky. I have seen a few in vietnam but yet to see any in thailand. Also remember that undercovers may try and sell you drugs and also dealers may dob you in for a cut of the bribe.
(*snip* Editied out unrequired info madmick19)
Enjoy your trip to these countries but be careful. I would recommend you steer clear whilst over here, there is plenty of fun to be had partying it up on the piss as well all the other delights of travelling to a foreign country. If you do choose to some words of advice.
Don't carry any on you around parts of the city.
Don't travel in a vehicle with drugs (check points can search you and the vehicle and your a target being a foreigner).
Drugs are less predictable here. They are more likely to be adulterated, or either bunk or very pure.
Don't let anyone wh sells you drugs give you a lift to your hotel.
Anyway, safe travels.