Hi:
If you use the Vista recovery disks, everything on the entire drive will be lost (the disks will delete all partitions, create a new one and install the OS, and I do not believe those disks will create a new recovery partition for Vista.
The recovery disks for my dc7800 wipe the entire HDD and just reinstall the OS on one partition and the few bundled programs that came with the PC.
I would imagine the ones for the dc5800 will work exactly the same, because the only major difference between the dc7800 and the dc5800 is an extra 5.25" drive bay on the tower model. Slight difference in the chipset too.