I loaded Win 7 64 bit onto a new 320gb drive in my Dell Latitude D620 laptop and I have been frustrated with the inability to disable the trackpad. I tried looking it up 6 months ago and gave up and I have been dealing with it ever since. The original drive had all of Dell drivers and stuff already installed on it. But Win 7 doesn’t.
So tonight I thought I’d give this another try and went to the bios and disabled it there but it still continued to work. I then went to Dell's website and download the input device Alps Pointer for my laptop so that I could get the driver back into my laptop. I then installed the driver in spite of the fact that Windows said there is a known issue with this driver. I clicked on the lookup issue on the internet but nothing happened. So I went ahead and installed it anyways.
After I installed it I went to the control panel, then clicked on Hardware and Sound, then click on the mouse tab and the interface for the track pad and pops right up under the device tab. Here you can enable or disable the pointing stick and the touch pad. It works great for me and my mouse is still functioning just fine. Finally after 8 months I have fixed this issue and hopefully it will work for you.