Well, he’d have to build the controller himself that will do the conversion from video to a serial stream. He’d have to write software to convert that serial stream back into image data on the PC. He’d have to write more software to interface all of that with his web server.
Not to be down on Mangetout, but that is a tall order for someone who is putting together what sounds like a hobby system.
Firewire is not an option; the range is not significantly better than USB (unless you use a repeater/hub, but the same can be said of USB).
Anyway, if I went for a firewire solution, I’d have to buy a firewire card for my PC (it didn’t come as standard), then pay over-the-odds for peripherals (cheapest firewire webcam I could find here is £50+ - I can get a USB one for less than a tenner).
Serial webcams are almost impossible to find, believe me I tried.
That is a fair assessment; I really don’t want to get too involved in the electronics of the thing and building it for myself would probably cost more than the USB>cat5>usb converters, which would give me the range I need.
Oddly enough, this question got asked on The Screen Savers last night. Leo managed to get about 17 meters using passive extender cables, but that was all the cable they had. Try checking techtv.com to see if they have a link up in the Show Notes (sorry, can’t link because I found this in the email newsletter.)
It may actually pay me to go for wireless after all; then I only need run the power to the camera; I’ve seen wireless colour cameras on eBay for a dollar ( 
plus ‘35 dollars shipping’ - AKA evasion of eBay final fee values).
I’ll still need a video capture solution, of course, but I’m going to need that anyway. the extra cost of the wireless version outweighs the extra cost and inconvenience of signal cabling.
I need to find out whether the 1.2 GHz band is unregulated here in the UK.
OK, 1.2Ghz actually turns out to be right in the middle of a military band here (I wonder if all the people buying the imported mini wireless cams know this…) there were no small inexpensive 2.4GHz (unregulated) cameras available, so I plumped for one that requires cabling (this one)
Will it be practical to extend the coax cable over something like 25-30 metres? If so, what sort of cable should I get?
It sounds like it may be simpler to move your house closer to the birdbox;)
I thought about your situation the other day when I picked up two of these setups but I thought you had solved it some time ago . The local Staples was remodeling and was cleaning out their overstock. This unit was new in the box for $ 15.00 each (originally $160-200). I flipped it on Ebay for 75.00 
. I wish I’d known you were still in the market or I’d have picked up one for you too.
Check the specified line impedance - it will be either 50 or 75 ohms. Now go over to RS Components and order the best quality cable in that impedance you can afford. For 50 ohm that would be 222-7566 (RG58, 50 meters.) You can get better, but it costs nearly five times as much per meter. Try this one first.
For 75 ohm, that would be 379-637 (RG59, 100 meters.)
Add a couple of RCA plugs and jacks to the appropriate places, and you should be in business.
Urk. Try 389-735 for the 75 ohm cable. The other is a thin cable with a high loss. Sorry.
This is true of FireWire 400, IEEE 1394a, but not of FireWire 800, IEEE 1394b, which has a maximum cable length of 10.0 meters.
Specs here:
http://lumbergusa.com/IEEE1394/2310_11.pdf
I don’t think that 10 meter 1394b cables are easy to find, but here’s one company in North America that sells them for 35 US$:
http://www.firewirestuff.com/cables1.html
Since nobody else has mentioned it, I figured I’d throw in a mention of the BirdVu bird feeder/wireless camera. It’s a bit pricey at $200, but it solves the problem quite nicely.
Some companies are making firewire cables that exceed the official 4.5 meter limit. Here’s one that makes firewire cables up to 10 meters.
10 metres still isn’t nearly enough though, but thanks for the info.
Thanks Mort Furd - I reckon I’ll be able to pick up a drum of cable on eBay once I know what sort I require.
I’ve recently become aware of wireless (802.11) webcams that might work perfectly for you.
Here’s one example: http://www.linksys.com/products/product.asp?grid=33&scid=38&prid=566
Thanks for that Mojo - they look expensive though - I’m not sure how happy I’d be leaving one of them unattended in my garden