TTL RGB ==> PC

Eventually I'll be shipping various 8-bit machines to the US, and was thinking of using a PC with a TV card as a display (most of the machines have UK PAL RF outputs, and I could add modulators to the ones that don't). However: - All TV card software I've seen has been utter crap, when it even works at all. - Typically there seems to be no scaling of the picture to fill the PC screen. - There's an obvious quality drop in the RF stages. - I'm warned that the digital tuners in TV cards often have problems locking on to the weaker signal produced by home micros. So... how about hooking straight to the TTL RGB outputs of the vintage machines and somehow sampling lines of data into the PC for display in a window (with appropriate scaling in software as/when necessary so that the image more or less fills the PC display)? Surely someone's homebrewed something like this already? I presume the speeds at which things need to work can be pretty high - but in theory it's just an RGB framegrabber but without all the analogue-type circuitry needed to decode a picture? I'm planning on shipping a few TTL RGB displays to the US, but maintaining them is going to be more difficult than maintaining the machines (and I imagine there are all sorts of pitfalls in taking a US-designed TTL RGB display and trying to use it with a UK-designed micro, as the frequencies involved won't be quite the same) thoughts welcome... Jules