External Hard Drive with Windows Data included in Time Machine Backup

I have data from an old PC that I am not going to replace loaded onto a NTFS formatted drive. It's just documents and things I can pick up maintaining and using on my Mac. I want this data backed up though and I haven't enough room on my Mac hard drive to copy it all over.

How can leave it all on this external drive (or I suppose on 'AN' external drive) but have it backed up. In a way, this can be looked at as me just extending the size of my Macs hard drive.

Does that make sense?

At the moment, because of how it's formatted, Time Machine won't let me take it out of the exclude list. And, I don't believe my PC will be able to access a drive formatted the way Time Machines wants it ... see?

Please advise.

Thanks!