I wandered round the stalls, and I only found one fan that looked close to what I was after: the Spire JACS07. It was £3, so I figured that it was worth the risk. Unfortunately, it turned out to be the wrong one; in particular, the power cable won't fit into the relevant socket on my motherboard. I've found a couple of possibilities at Overclockers which look more encouraging:
Zalman ZM-NBF47 Fanless Northbridge Cooler (£8.04)
Akasa AK-210 Blue LED Chipset Cooler (£3.44)
I like the idea of the Zalman one (since it will be silent), but I'm not sure whether there's actually space for it to spread out between the other components on my motherboard; it might bump into the CPU or graphics card.
For now, I've just unplugged the fan, so that it will stop making such a racket. That's not ideal, but the heatsink is still in place, and random people on forums seem to think this will suffice if I'm not actually overclocking (which I'm not). I'll order a replacement soon, then I'll have to work out how to remove the current fan; I suspect that I may have to take the entire mobo out of the case, which is a pain in the arse, but so be it.
While I was at the fair, I also bought an "All-in-one card reader" (internal, fits into a 3.5" drive bay). This is something I've wanted for a while, and it only cost £5, so I figured it was worthwhile. There are several models, and since they work on USB they should be compatible with any modern OS, but I chose this particular model because it was the only one which explicitly mentioned Vista on the box. When I got it home, I found a slight hitch: I don't have any spare USB sockets on the motherboard, so I had to unplug the rear card (2 sockets) before I could plug in the card reader. That's inconvenient, but not disastrous, because I shuffled my cables around to use other sockets.
I want a reader for CompactFlash cards, which my digital camera uses. In the past, I plugged the camera into the computer; that was fine under XP, but it doesn't work with Vista. Also, the camera needs to be turned on while I transfer photos, which drains the battery, so it's much more convenient to just pop the card out. Once I turned the computer on, it showed four new drives (one per socket in the card reader), so I put in my memory card to test it. Unfortunately, it didn't recognise the card. Also, I realised that there was no way to get the card out! In the camera, I slide the card all the way in (so that it's flush with the surroundings), then there's a button thing to pop it out. In the reader, there isn't, so I had to take the computer apart again so that I could retrieve it. It turns out that you have to be careful when you slide it in; three of the slots are completely enclosed, but the CF one isn't. I had it tilted slightly upwards when I inserted it, so I missed the pins at the back and wound up with the back of the card resting on top of the reader. If I put it in properly, I can copy files off, and the card sticks out of the reader so that I can pull it out again. This isn't a perfect solution, but it's better than what I had before.
While I was poking around in the case, I decided to remove my video capture card. It worked fine under XP, but Winnov never released any Vista drivers; they no longer list it on their website, so it seems unlikely that they're planning to. This being the case, it's not doing me any good, so it might as well go to a good home. Would anyone else like it? It's a PCI card (Videum Conference Pro), with S-VHS/MXC/composite inputs, as well as microphone/speaker ports. It comes with a webcam (320x240 resolution). I no longer have the original packaging, but I should have the manual/CD floating around here somewhere.