Depending on the Dell partition, you may not be able to delete those using conventional windows partition software utility. Not even Partition Magic will delet or change the Dell special partitions. There are some tools I have used that will quickly revert your hard drive back to factory defaults; give you a complete erase of all data and reset all switches.
Do a Google search for "Ultimate Boot CD" and then use the utility called MHDD to reset the drive to factory defaults. This dumps the boot sector and other Dell proprietary partitions as well. You end up with the drive as it was new from the factory with nothing on it.
Now, having told you that, I have to advise against using a laptop hard drive in any DVR service. These small drives aren't really designed for this type of service. Even if you do have a 7200 RPM drive, the I/O may not be fast enough and the continuous write that DVR service does will probably cause quick failure of these drives. This is just my opinion so give it a try and prove me wrong. I'd be fascinated if you have success with it. Some of the most recent 2.5" drives may stand a better chance but older ones were, IMO, just too slow for video DVR service.