Although... if I made up some exact square section things out of plastic sheeting or whatever*... that would look immensely cool
and probably work better, as I could make everything the exact same size as the fans in use. Here's the plan:
PSU - fairly obvious, standard thing I expect. In the top of the case, into the back of the PSU and out.
CPU - I have one of those tower heatpipe things, with a fan going through it sideways. So I can basically do something roughly following the shape of the PSU (maybe even the same intake?) and going out the top of two 80mm fan holes in the back.
Graphics - In the lower 80mm hole, over something like a VM-101 and out of the spare expansion holes above the card (it's PCI-e)
This just leaves the northbridge, HD and ram. I'm thinking maybe of doing them in one - coming in the front fan, over the HDs, up across the NB, past the RAM and out of the case top. The ram slots and nb are almost perfectly in line, so this might work. Alternatively I could cut a hole in the side panel at the bottom, taking a duct just up over the nb and ram. Then one next to it taking the air from the front fan and HDs.
Hmm quite a ramble, I was only going to ask about the flex stuff, but I probably won't use it anyway if I'm trying to go over little heatsinks and stuff!
Any thoughts?
*I don't know what this stuff called. Imagine... the little artist header cards you get behind CDs in a music shop. That kinda thing! I figure it'd be fairly easy to work with. Just need to remember some geometry to cut it all perfectly
That said, is there anything else you'd recommend? It doesn't need to be solid.. just be able to hold it's shape when glued into a box.EDIT: on closer inspection of the layout, it's probably more sensible to take a duct from the side panel, over the VM-101 and out of the lower 80mm rear hole instead
I'd take some photos and draw on them if I knew where my camera was! I should only have one extra fan than normal - the one cooling the NB and RAM, and that's if I decide to have them seperate from the HD. SO noisewise this should be good, and hopefully very cold since everything's getting fresh external air EDIT2: I guess as long as everything is like... in parallel, it doesn't matter if any ducting is shared? I mean... I can have the same intakes and exhausts, so long as it splits either side of the components. So on that basis, the air could come in the top of the case for the CPU, through the cooler, and join the exhaust from the VGA duct, over a fan. This would increase CPU cooling too. Although I suppose decrease the VGA cooling, as some of the fan's airflow is being "stolen" by the CPU. Maybe that's a better tradeoff though, as the CPU is likely to generate more heat?
EDIT3: I'll be impressed if anyone reads through all this
I've just seen that silverstone TJ06. Quite a price tag, but most of the work done for me All I'd need to do is:- join a duct from the VGA card to the end of the main duct next to the 120mm fan (possibly with a fan in it)
- mount my single hard drive in one of the floppy bays, or 5.25 bays in a silentdrive
- duct the 80mm fan onto the northbridge
- cut through the now empty hd enclosure for a main case exhaust
OR
- cut through the now empty hd enclosure, seal off the bottom of it, thus isolating the PSU
I've never had a problem with HD heat, but if I do, it shouldn't be hard to fit something there.
Only problem I see is with the ribbon cable going from my soundcard to it's front box (terratex DMX 6fire) but I can easily extend that
etc) out of the way, then a single slow fan will be more than enough to cool the drives, NB, RAM etc. 
