There's no problem here that I can see. Press D to delete the existing C partition and install to the unpartitioned space.
Your Mini 9 has an SSD - baking it isn't going to help.
The BIOS saying zero size is interesting - this is usually a symptom of a failing SSD and yours is the original as shipped by Dell in 2008-2009. That the XP install can see it, though, suggests to me it is still working.