Need help/advice in using '09 27" iMac as ext. display

Hello, new here, but I have a question that I thought this community might be able to help with.

I have a late '09 27" iMac. I love it, and I would never directly replace it, but the gamer in me gave in to temptation and sprung for the recently announced Alienware X51 gaming PC. Distasteful as that is, I'm hoping to treat it more as a gaming console, in that I'm ONLY using it for gaming. And as I live in a one bedroom apartment, I'd love nothing more than to use my iMac as its display.

Now, I know this kind of goal isn't anything remotely new, and I wouldn't be posting a new thread for it if scouring the internet turned up a definitive answer. There's a lot of conflicting info out there. I know the iMac can go into target display mode using either at least a mini displayport-mini displayport cable or a mini-regular displayport. My understanding of the X51 is that it uses an HDMI output, rather than a displayport, DVI, or anything else of the sort. Unless I'm missing something, naturally.

Based on my research so far, it looks like I'm cooked and I'll need to pony up for a second display, but could anybody confirm this for me? I know mini displayport-HDMI cables exist, but so far haven't had any luck in determining if that sort of thing could actually work to activate target display mode, or if it'd be a waste of money. Similarly, are there any sort of viable converters of any kind out there that I'm not seeing?

Anyway, any help or advice would be greatly appreciated. Getting a second display wouldn't be the end of the world, but saving 150 bucks and some space would certainly be nice! Thanks in advance.