Okay, I tried all of your advises and I thought the best and easiest way was to reinstall the whole system.
I used the "IO80211Family" kext.
I used this guide, and according to that I can get the WiFi up and running.
Thanks for your answers and if you know how to get the WiFi working, post a replay.
I recently installed OS X Mountain Lion with MyHack on my Dell Latitude E6400. Everything but the WiFi was working so when I installed the wifi kext with Kext Installer, it won't boot anymore. When I boot with -v it hangs at [ PCI configuration begin ] I've tried to delete the kext with terminal from the usb stick I installed from, but it didn't help. When I boot normally the spinning wheel below the apple logo just stops. Here's my computer specs: CPU: INTEL CORE 2 DUO P8600 GPU: NVIDIA QUADRO NVS 160 WiFi: INTEL WIFI LINK 5300 Bluetooth: DELL WIRELESS 370 BLUETOOTH Full specs: HERE (click on System Configuration in the blue menu in the middle)