First you must get 1,950 points or more. Go in the help room so you can get a flamefrower and any gun you like(reason for this is incase you run out of ammo).

Next you get 1,000 more points and go upstairs (you should be on about round 3-7, if you are on 7 you best be quick they go really fast) then as you come up go left twice at the top and you should be in a corner. If not look for a small corner, now look at the floor and you should see a log thing next to the wall (not the bannister). Walk away for about 3 seconds, then run up to it. When you are on it jump and when you are about to touch the ground lie down, now try to stand up. If you can it is wrong so try to do it again. If it does work it will say "can't stand here".

Now, don't let the Zombie go in a huddle because they can push each other into you and dont throw grenades as the Zombies turn into crawlers and crawl into you and start biting you. There will be a pillar there and the Zombies will hit the pillar come back to you and you will die.

I would use your second gun first, then the flame thrower.