Hi guys,
I know this sounds like an advert, but it's not: I work for a Web Hosting company.
I found a very cool USB device from Lew Engineering called RCJoy. It works with just about every PPM transmitter I've seen and makes it appear to the system as a multi-axis joystick/games controller.
Supported operating systems include: Win 98, ME, 2000, XP and even MacOS/9 (if you're that way inclined).
It's probably a little more expensive than building your own interface, but at least you don't need to build and debug it yourself (plus it works with modern notebooks without having to buy a docking station to get a joystick port).
There's lots of information about it on their website, including a freely downloadable Acrobat PDF manual so you can get the low-down. If you're interested, check it out:
Kind regards,
Anthony.