You can call HP and request one. If you configured the system online, shame on you for saving $5 on not selecting the DVD for the OS.
Alternatively, if you have a friend with a Technet subscription, you may be able to pester them into downloading and burning a copy for you. Check with your lawyer first, but I don't think there's anything to worry about since it's just media and not a license.
Using the Technet DVD, you will want to cancel activation during the installation since it will fail immediately if you enter a retail or HP OEM key, but will activate just fine using this same information once installation is complete if done manually in the control panel.
Learned this the hard way when I was shipped Win7 Pro 32-bit media with my Ultimate 64 license via a reseller program. For the first time in a couple of years, I was happy to have forgotten to cancel Technet.
Just don't torrent OS media. Legal stuff aside, you don't want your new copy of Windows to come with a backdoor.