802.11b is rated at a maximum of 11Mbps. If it doesn't have a strong signal, it will drop to about half that. And then about half that again if the signal still isn't strong enough. You would expect to have a strong signal if the PCs are in the same room, maybe less if there's several walls between them. Even with a reduced signal, the network card would still be faster than most people's internet connection speed (currently most people in the UK are on 512Kbps to 2Mbps).
Having said that, I'd weigh it up against the fairly minor extra cost of going to 802.11g, which is up to 54Mbps, and probably opt for that as it will last you further into the future as your Internet connection gets faster with improved ISP / telephone provider technologies.
For a fuller description, here's a link to a really useful web article:
http://compnetworking.about.com/cs/w...11standard.htm