I want you to try something for me.
Try using a wired external mouse (non-Microsoft model) and see if that helps.
Your situation is different, becuase it's a laptop, but my Win7 64-pro desktop began experiencing the same exact issues as of a few months ago. It had been fine for several months.
After reinstalling Windows, testing my ram, and multiple other possibilities -- all to no avail -- I came across several threads where people complained that their mouse/keyboard set-up was not compatible with Windows 7. Apparently, this is a growing issue and there are literally hundreds of complaints. In my case, it was a Microsoft wifi mouse/keyboard set. I tried using a wired mouse and keyboard (pilfered a Samsung one from my work computer) and guess what -- no issues in 2 days! Others had the same results.
The difficult thing is this -- the work-around is using a PS/2 port mouse and/or keyboard. You have a notebook. Guess what, you're not alone, and I've seen it mentioned that several Dell notebooks are experiencing this same issue with Windows 7! More than one person mentioned having XP and Win7 dual-booting on their machines, and the problem only happens in Windows 7.
You can try a wired USB mouse, as PS/2 is not an option with a notebook. Some mice have the problem, others don't. See if that helps. Sadly, your computer may actually have this problem with Win7 unless Dell can come up with a solution for why their mousepad is tripping this issue in Win7, just like many other mice are.