http://cashflowlogic.com/iPhoneJailBreak.html
MAKE SURE OF THE FOLLOWING:
1. You are an unmoddified 1.1.1
2. You do not have iTunes open
3. You have the iJailbreak FOLDER installed in your Applications folder (and it has a "resources" folder inside it
4. You run the Safari crash without unplugging and plugging in the iPhone (leave it plugged in the whole time)
5. You do not do anything else with the phone after it crashes
6. And maybe as an extra step, you restart the phone before you start all of this.

MAKE SURE OF THE FOLLOWING:
1. You are an unmoddified 1.1.1
2. You do not have iTunes open
3. You have the iJailbreak FOLDER installed in your Applications folder (and it has a "resources" folder inside it
4. You run the Safari crash without unplugging and plugging in the iPhone (leave it plugged in the whole time)
5. You do not do anything else with the phone after it crashes
6. And maybe as an extra step, you restart the phone before you start all of this.