Don't worry, we're not afraid of viruses
After doing some research, I found these chipsets to be quite similar, but there are some differences:
P4M890 is both s.478 and s.775 compatible. It also features an on-board UniChromePro graphics controller.
PT890 is only s.775 compatible. No on-board graphics here.
Either ways, both chipsets use the VT8237A southbridge, which means SATA1 support, 10/100 LAN, and most importantly - very poor overclocking capabilities because of missing PCI locks.
Even if you try crossflashing it with the Foxconn BIOS (which I strongly disapprove of), don't expect any success with overclocking.