help? i need to know what's the title of this PC Game.

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lol. this is crazy. but i played this game 13 years ago. while i was in the computer shop this afternoon, i happen to see one of the crews playing it. unfortunately, i was in hurry because it was raining and i need to get home since i have lots of school work to do. so here goes: i remember playing this game. it's a very classic PC game. internet has just started at that time. when the game start,you can the character stands outside the gate. he wears a hat and he carries a shotgun, and i think i am pretty sure he wears a red pants. =) once the character jumps up in the gate. there's this house. inside the house, there are a lot of zombies. his mission is to get on top of the house. then, once he reaches the top, there's a mastermind for the first level. same goes with the second. i think the third level is with the slimes. then the fourth one is where you encounter the level 4 master which is a half horse-half human. i hope there's any of you who have played this game. lol. bear with the hassle. i am looking for this game. kind of makes me remember my highschool days. =) have a nice weekend guys. =) and thanks for your time in my silly post. lol