Using WLAN from computer to computer doesn’t work in practice for some reason. The transfers progress in bursts with long pauses between which means that they are very slow. Downloads from the Internet are a lot better and progress smoothly without bursts.
This is probably a problem with my Linksys WRT54G. In my opinion it is a worthless piece of crap. It needs resetting at least once a day when there are more than one computers connected to the network as it very often just freezes.
Maybe it is time to start looking for a replacement.