The Mac problems, apart from printing via the network, are now sorted. I got a printer driver and can print to the laser via USB so it isn't a big deal, but it's annoying.
The encryption problem solution was stunningly obvious once spotted - the router was using an ASCII key while the iBook was sending it as hex, which is easy to change in the iBook menus. File access via WiFi also turned out to be easy to fix - I didn't have AppleTalk enabled on WiFi. Means I have to switch it off for ethernet, so I won't do it unless I have to.
The network printing thing is odd - the iBook now knows that the printer server is there, since I've enabled Appletalk on it, but it doesn't seem to be able to get the idea that it's linked to a printer - it's just showing as another local site, but nothing happens when I click on it. Can't seem to share the inkjet at all, but it's not something I'm much worried about.
Apart from that things are going reasonably well... which probably means I'll be hit by a meteorite or something.
Someone at work put me on to a company called Primark that sells VERY cheap clothes - e.g. £4 and up for a pair of jeans, compared to Marks and Spencers £25 or more. Went to their Hammersmith branch on Wednesday evening and got four £6 pairs of jeans, two sheets, two belts, five pairs of socks and a T-shirt for 40 quid or so. No idea why I've never heard of them before, but they have a LOT of branches and the quality seems good. My sister turns out to be an old customer, and warns that I got lucky by going on Wednesday - it's their quietest time, and I still had to queue 10 minutes or so to pay. Their web site is http://www.primark.co.uk