My wireless card works fine in 2000. Look online to see if there's a 98 driver for your particular card. If there is, then download it, use the hard drive swap method to copy it to the laptop. If there isn't, you still have to swap out the drive to install a new OS. Windows 2000 is pretty good (it came on my [used as well] IBM Thinkpad A21p with Pentium 3 850MHz 512MB [I upgraded, came with 128, but still worked well]), I installed it as well on my old Celeron 500 desktop with 256MB RAM, and it worked fine.
You could also think about using Linux on it, but wireless cards (especially Broadcom-based ones) are a pain to set up (possible, I'm using one now, but it was quite a challenge to set up).
Remember that you're probably going to have to install the OS from a desktop, so be sure to download all the drivers for the laptop's hardware and copy them to the drive before you return it to the laptop. Once it's in the laptop, you'll have all the drivers you need to install the rest of the system.