If you "upgraded" it to XP, I assume it had Win98, which suggests this laptop dates back to the days when network adapters were not commonly built-in. You usually had to use either a PCMCIA/PC Card, or perhaps a USB network adapter. So you should be able to dig up, maybe off eBay.
P.S. I'm not sure what you're seeing under hidden devices, but I assume it's not a usable network adapter. It might just be a virtual network adapter, perhaps a WAN Miniport from some other piece of software, e.g., AOL. If so, the prior owner probably had a network adapter installed at one time and pulled it before selling it to you.