This is untrue, I know you could do it Home Server 2008, so just because you do not know of something do not post an absolute.
From the Apple support article link below:
The most common format for a Time Machine backup drive is Mac OS Extended (Journaled) format, but Time Machine also supports Mac OS Extended (Case sensitive, Journaled) and XSan formats.
I know exactly what I'm talking about.
From the article:
Time Machine can’t backup to an external drive that's connected to an AirPort Extreme, Time Capsule, or a drive formatted for Microsoft Windows (NTFS or FAT format). If you select an NTFS or FAT-formatted drive, Time Machine prompts you to reformat the drive.
Eric beat me to it.
Just to expand a bit. Your Home Server 2008 solution worked because it's a server. With AFP on at the server (Apple Filing Protocol), the Mac sees it as a native drive, regardless that the drive isn't actually formatted for the Mac.
What you asked was if you could share an NTFS raid setup. The answer is no. You are not running a server and the Mac will see any partition you try to use for TM as what it is (an NTFS partition) and want to format it.
Yes you can make multiple backups on one hard drive, for example if you’ve 1TB hard drive installed in your PC and you’ve two Mac Machines with 500GB drive each then you just make two backup images with size of 500GB each.
Your subject states: .... make my Windows PC the location for my TM backup.....
According to the SLA, you are only allowed to run Mac OS software on Mac hardware. You are allowed to make one backup (see para. 2 I for restrictions):