That small 5gb partition is where they store all the software for the default build. If you hose your drive, you can get it back to a default, fresh-out-of-box state using the partition.
Unfortunately I've forgotten what you do to get the re-install started.
Through several attempts at restoring/re-installing I've concluded that my HD drive is bad, and I don't need the other two partitions. I guess the 55mb partition was probably the diagnosics.
For all practical purposes, Dell is wasting a bunch of space for people who don't know how to install an OS.