stuck at beginning of game

[dll72]

I just bought Half life and alredy I am at a stand still. I haven't made it to the top yet. I have only a crowbar and just received the pistol. The part I need help with is how to get past the broken bridge. It is broken on both ends and has a scientist standing in the middle of it. When you climb aboard the bridge, it falls unless you kill the scientist 1st. Even when I do that, I still can't jump to the corridors to the left or right at the other end of the bridge. Am I supposed to be able to do this or is this just a decoy and I am supposed to be going a different path? Please help the helpless

the only point in that area is to get the geek to give you a shot if you are hurt. Head to the control room and crawl through the broken out grate near the floor. After killing the two crabs and recharging at the 1st aid station climb up the broken pillar in the corner, go through the hole it created and get to work...let me know if you still can't find what I am saying....