From what I understand: the 'Recovery drive' feature (D

is something
provided by the manufacturer of your computer (like Dell or HP), as a place
for your system to make Restore Points. and not something designed by
Microsoft or Windows or Vista. But Vista, per se, looks around for likely
destinations for your 'automatic backup' and sees this apparently available
separate 'drive' called D:, observes that it is different from your main
hard drive (C

and suggests it as a location choice for your automatic
backup. One could say that Vista, per se, does not know that HP has set up
this D: drive on the same physical disc as the C: drive.
So, how do you know that you do *not* have use of your Recovery Drive (D

?
The intended use of the recovery drive is for System Restore points; is D:
working for those? Perhaps a first thing to do on that is to check and
see whether your system has been making regular Restore points. On your
Start button, type System in the search box; then click on System Restore;
if you are prompted for an administrator password or confirmation, type the
password or provide confirmation by clicking Continue. In the System Restore
window that comes up, click on Next. This will give you a listing of all
the Restore Points for the last 5 days; if you want to look further back,
click the box for "Show restore points older than 5 days". My system has
Restore points about every day, and additional ones when there has been an
event like a Windows Update. The question at this point is whether you do
have one or more Restore points listed. If you do not, what *is* listed?
If you have several recent Restore Points, then your D: is working as
intended.
Keep in mind that it is *not* recommended that you use the D: drive as a
location for Automatic Backups, even though D: is given as one of the
location choices. Keep your D: drive strictly for System Restore points.
Check and see what you have and write back.