Do you, or your friend, have a copy of XP Media Center?
He most likely didn't get any discs at all. Lovely HP and their Recovery partitions - to better serve us. All this so HP can cut down on their tech support staff budget and save $3 or so for the processing of cd's for each unit.
Bottom line foolish, because they turned a lot of people off. Future business from the main stream public will plummet. Not a big fan.
Even though your friend has turned off XP's Restore system, I'd be willing to guess that HP has set something up behind the scene to add images to that partition. Has to be a reason why it's expanding with no one knowing why. Would like to hear from techies with more intimate knowledge than I. Reworked a couple dozen of these last two years because the business customer wasn't happy about the support hassle of these setups.
How big is that "D" drive? The one's I've come across were 8g. And, how long has he had the unit? With only 32mb left - that's close to an additional 4-5g been written since new. Is this machine becoming a problem?
As to accessing the "D" drive, he has documentation to walk you through it.