You should probably ask this question in the Netstumbler user forums.
For Windoze 98/ME, only a limited number of Orinoco/Lucent/Agere/Proxim cards with Hermes chips are supported in version 0.3.30. Version 0.4.0 does not work on Windoze 98 and ME.
For W2K and XP, *ANY* device that has an NDIS 5.1 driver will work with version 0.4.0.
Linksys uses a wide variety of chipsets in a wide variety of products. It would be helpful to know which one you're considering.