Hi Mike!
Sorry for your dang luck!
I'm no virgin when it comes to installing a new OS to a computer. Been there, done that, got the tee shirt, coffee mug and ashtray.
I'm glad that psychological scars are not real scars, or I'd look like Frankenstein's Monster.
Installing a second OS on my computer still makes me shudder. I check, double check and then triple check, to made sure my main OS Drive is disconnected, to prevent it from being corrupted. I've loaded Win-7, Peppermint and now Win-8, all to separate hard drives.
If I get tired of an OS, I just wipe that drive and put something else on it, never in conflict with my main OS.
OK, down to business.
Win-8 DP will install as an upgrade, from boot on, if it sees another OS in the system.
I tried for hours to install W8DP on an old Compaq desktop PC, about 6 years old.
I disconnected the original IDE drive, to preserve that OS and connected a newer and larger SATA II drive to an available port on the mobo.
I guess Compaq was too cheap to put in a SATA II hard drive.
Anyway, the SATA II drive had some OS on it, not even sure right now, which one. But, W8DP tried to install as an upgrade to that older OS. I could not make it do otherwise. We fought, I lost. (Oh Crap!)
So I took the high road..... I booted up the PC with my DOS Utilities CD, ran FDISK and removed ALL partitions from the disk and let FDISK create just one partition on the drive.
With that done, W8DP installed without any more jerking me around. Now for the clinker..... the only version of W8DP that I have is the 64 bit version, but, it installed without a whimper on the old 32 bit Compaq and runs like a champ.
It installed video drivers (generic) that allow 1024x768 resolution, but it didn't have sound or lan drivers for the old mobo.
After hours of Googling and digging through my own archives, I finally got both the sound (AC97) and the LAN working.
I still have not found updated drivers for the SiS Graphics chipset on the mobo, but that's OK, the generic drivers are working OK.
I've been in communication with several other guys who have also tried to install W8DP on a drive with another OS and they have had similar experiences to mine. When they took my advise and loaded it to a completely BLANK HD, the install went off without a hitch.
So, that's my tip of the day. If you have a spare HD laying around, wipe it clean and use that for your W8DP install.
Do not let the installer see your main drive and your main OS, maybe by unplugging your main drive, during the process.
Happy Holidays Everyone!