There is a working work-around for this problem. (
credits go to TheKennedyCurse :-)
This problem occurs when you did the quest where you need to get Mc Gregor's hat and bring it back to that chick at the Atomic Wrangler.
You might notice when you take his hat of his body, his hat is still visible on his head (and I think that is the reason the game crashes).
To solve this, go to and enter the Crimson Caravan. Go forward until you see on your left a tent with supplies (this is in the open by the way, not in a building).
Next to the 3 medkits, there are 2 hats. Crouch so you are stealthed and take the Old Cowboy Hat.
Travel back to the North Gate of The Strip. Equip the hat and enter the gate. Normally you can now enter The Strip again.
So basicly, you will always have to equip this hat when you enter The Strip if you don't want the game to crash, but there is a better way (notice that this
DOES NOT always work!!!)
Search around to find the body of Mc Gregor. When you find him, put the hat on his body (
NOT on his head!).
This way you don't have to wear the stupid hat every time you want to enter The Strip.
Like I said, this doesn't always work. It worked a couple of times, but for some reason the game started crashing again...
When it keeps on crashing (and the hat is locked in The Strip), there is a spare Old Cowboy Hat located in the Powder Ranger Camp West.
It is located inside the camper, in the armor case. Powder Ranger Camp West is located right below Joan Sky Diving, and to the right of Goodsprings Source. (
credits go to Jerfer for this 
This way, you have the hat on the body, and have a spare hat in case it starts crashing again.
Alright, that's 1 problem fixed, 4999 to go :cryvaultboy: