If you have a PC laptop, you will need to get a PCMCIA wireless networking card.
If you have a newer Macintosh laptop, you should consider an Apple Airport card, which installs inside your computer.
If you have a PocketPC handheld, and you have a Compact Flash slot in it, you can use a Compact Flash wireless networking card.
If you have a Palm or Handspring handheld, there are specific solutions for these devices as well.
In all cases, what you are looking for is 802.11b compatibility, specifically stated.