you could use any vista DVD to get to the repair settings. you could just download one of the Vista DVD's online and just not use it to install non-geniune Vista on PC's. Only for the repair options. should be the same right? (link above looks like its what your looking for though, and no problems downloading a illegal version of vista)
if you DO need the HP dvd:
If you really need to, you could probably get HP to send you a backup disk. I have an HP laptop and the hard drive failed on it. At the time it was believed to be a software problem, hard drive passed the hard drive tests? So I was told to restore it, I could not restore Vista because the recovery partition was corrupted. I was informed by the HP help desk that I should have created my own backup disk. I had just assumed that I had a disk already that was shipped with the PC (like most I have had before). None of the paperwork ever said to burn my own DVD, and when the recovery partition failed, I was told I was out of luck. Luckily for me, when I asked for a supervisor I got them and I had a DVD shipped to me for my laptop (Vista Home Premium).
If you go to HP and explain the same sort of thing, you should be able to get a disk sent to you. This is if you need to do a complete restore though, that way its back to HP's core install.