Hi Nielsen,
5 Series chipset is just fine with Windows 8, although 8 is a total waste of time in my opinion.
Your unknown device is probably the SOL (serial over lan) of the Intel(R) Management Engine.
Simple fix really once you know what it is.
Let me know what platform (Model notebook, mainboard, etc), if you can't find it and I'll assist.
Dell's file is SWB_DRVR_ME7P1_5M_7_1_52_1176_A04_setup_ZPE, of course the key here is the ME7, Management Engine 7 (Windows 7). It will work just fine with Windows 8. Because just as Windows 7 is Vista with the problems fixed, Windows 8 is Windows 7 with a retarded look!
More personal opinion....And for you Windows 8 fans out there that plan on bashing me, I don't care...