Windows bootcamp file path on 2008 Intel iMac
The problem here is you are not specific about what you mean by "My imac hdd is starting to go." Being specific and detailed will always get you a better answer.

That said I can (hopefully) infer that there is some sort of error that has messed up a computer's ability to actually read the drive. This could be something as simple as directory corruption (reparable with something like Diskwarrior, Drive Genius or Tech Tool pro) to an actual physical error with the drive mechanism or circuitry.

The fact that neither a PC nor a mac can read the drive indicates (at least) the former. And trying a commercial disk repair tool would be my first suggestion.

Also Boot Camp actually partitions the hard drive and segregates all Windows files on a partition completely separate from the Mac O/S files. So when you boot into single user mode you are booting into the Mac O/S and browsing the Mac O/S partition.

There may be a way to mount the Windows partition in single user mode, but I just don't know how.

When you connected your iMac as an external HD (target disk mode) did your PC even see the Mac's drive? You would know by right clicking on the computer icon and selecting MANAGE. then go to disk management and look for the Windows Partition on the Mac drive that you just connected. I have never tried this and am not even sure if it will work.