virtualbox.org

Tried "recommended update of VB, but now get msg:

Could not start the machine CS50 Appliance 19_1 because the following physical network interfaces were not found:

Realtek RTL8139/810x Family Fast Ethernet NIC (adapter 3)

You can either change the machine's network settings or stop the machine.

I'm using WinXP-32bit system. There was also a msg that appeared during installation that indicated that the update was incompatible with WinXP.
I have little idea of what to do from here, so hope someone can help.Should I download the above-mentioned driver? If so, where does it get installed? Step-by-step would be helpful

No you shouldn't. What you should do is to go to the "VM settings" -> "Network". One of the adapters is "Attached to: Bridged adapter". The place that you got the VM from had a Realtek RTL8139/810x card. You don't. You either have to select the NIC from your physical computer, or not use the adapter, or change it from Bridged to NAT.

thanks; changing from "bridged" to "Nat" solved the problem. By the way, does this upgrade now allow "Suspending" the VM instead of the need for "powering off"?

Upgrading without powering off will ALWAYS be a bad idea, regardless if the software allows it or not. I wouldn't try if I were you. Keep it clean.