I just found this game and finished it within 1h, dunno how so many people encountered bugs, since I didn't find any.
And because of the fact that this game is 10 years old, I guess it is time for a medal walkthrough, for all those finding it like me and struggling to get them.
If you want to find them yourself, I advise you to not read further, I won't force you to read it anyway. So here it comes.
How to get the medals:
1. Big wet juicy kiss - find NeNe in level 5 (the one where you go down a long elevator and see a chicken on a toilet). Before exiting through the levels exit door, walk back to the edge, fall down to the hidden area below and shoot the first crate you come across. NeNe is inside.
2. self-explainatory. Just win the game.
3. Twice the fun - find Darnell in level 8 (the second railroad-level). At the beginning jump over the gap that you're supposed to fall into, walk right and shoot the box in the corner. Darnell is inside.
4. Dude it's my turn - in the first level (with killable NPCs) walk right instead of left and press E in front of all 3 gaming consoles.
5. Meat is murder - beat the game without killing a single enemy, the medal pops up before the boss. The corpses on the railroads don't count as kills, so it's ok to drive over them.
In order to do this hardest of all medals, play through the game jumping over all enemies. You can walk past the big chickens with hammers. With the shotgun chickens, wait until they scream before jumping over their shot and walking past them. If you walk straight through, they will hit you once you pass them instead.
6. Vulgar display of power - kill all the NPCs in the first level
That's it so far, have fun and don't whine about any bugs anymore. There are pretty much none. If there are, it's your PCs fault. And after 10 years nobody would bother fixing this, so save the time for something different :P