My hardware "scrap pile" contained a Dell Inspiron 530 - not the most glamorous of machines and rather out of date and old, too, but it works and it runs a few pieces of software that I don't want to reboot my Mac for regularly. Problem was, I had to rebuild it because it had multiple OSs installed and none of them worked. Note to self - don't mix 32 and 64 bit Windows on the same partition and expect it to work flawlessly.
I did still had the recovery partition, but it wasn't accessible from the boot menu any more. Normally you're supposed to use the advanced boot menu to access it. I couldn't figure out how to boot into it. There is a Windows folder on the partition, but no obvious boot loader. I also didn't want to pay Dell for a set of recovery disks, mainly because those would have cost more than the machine is worth to me.
Poking around the recovery partition showed a Windows image file that looked it contained the factory OS setting - its name, "Factory.wim" kinda gave that away - and the necessary imaging tool from Microsoft, called imageex.exe.
All I needed was a way to actually run them from an OS that wasn't blocking the main disk, so I grabbed one of my Windows 7 disks, booted into installation repair mode and fired up a command prompt.
After I made sure that I was playing with the correct partition, I formatted the main Windows partition and then used imageex to apply Factory.wim to the newly cleansed partition. This restored the machine to factory settings even though I hadn't been able to boot into the recovery partition to use the "official" factory reset.
Oh, and if the above sounds like gibberish to you, I would recommend that you don't blindly follow these vague instructions unless you want to make sure you're losing all the data on the machine.
As a bonus task, you also get to uninstall all the crapware loaded on the machine. Fortunately it looks like everything can be uninstalled from the control panel. While you're installing and uninstalling, make sure you update the various wonderful pieces of software that come with the machine as they'll be seriously outdated.