I posted this last year in response to someone's query on a similar topics:
"We have a desktop on XP Home, and a laptop on XP Pro, which came with 802.11b built in. I got a Linksys USB11 .11b adapter (approx £50) for the dt, enabled ICS on it to share the broadband connection, and set the printer to share. The young un can wirelessly surf and print, all works fine, for £50 cant be bad. Points: 1. This is called an ad hoc/peer to peer set up. The dt needs to be on all the time. Otherwise you're looking at adapters for each, plus an access point. 2. Your firewall MUST be configured to allow the remote kit to get access. 3. WEP adds additional security preventing any passing tosser outside to use your network. 4. Despite the hype, set up isn't straightforward, I think due to the many different ways it can be done. Gaz's suggestion of using XP's wizard takes some of the aggro out of it.
Good luck !"
Part of the rationale then was that we still had the original Speedtouch adsl USB modem supplied by BT, so I wanted to do it as cost effectively as possible. I'd probably go for an 11.g adapter now (similar price anyway) as 2 more laptops we've bought since have 11.g built in. However, I have to say that for surfing & printing, 11.b is fine. I'm keying this in the lounge on the wife's lappy, the main machine & modem being about 20' away.
To sum up:
1. Wireless for 40/50 quid.
2. Desktop needs to be always on.
3. The d/t firewall needs to allow access.
4. Set ICS/File/printer sharing as reqd.
5. Set up encryption if you can.
6. SP2 gives more ease/stability.