Have read through all the post and must admit the dscaler application is the best option for pal gamecube owners to connect the console to the computer.
I just want to warn you, stay away from these so called 'VGA boxes'. In most cases they are just cheap scan doublers and only provide inferior signal/picture quality.
TVs use a technique called Interlacing, which means that a screenrefresh only refreshes every second line on your TV. So in the first pass, the odd lines are refreshed, in the second pass, the even lines. It takes two passes to refresh all the lines. The reasons for doing things this way are complicated and again, nothing to worry about.
You may have heard the term "progressive scan". This means that all of your screenlines are refreshed in one pass and not only half of them (Thats the way computer monitors work). The scan doublers read the original video signals (mostly composite) into a solid state memory at the original frequency and, almost simultaneously, write this signal out again at twice the original rate. The output signal is processed to be made compatible with standard, low-cost and easily available monitors used with current PCs.
Ah yeah scrap the default software which comes with your TV card. Most times it doesn't even make use of all the features of your hardware. So it isn't possible to switch into pal60 Modus (which provides clearer images 'cause of the additional ~160 lines) using the Win TV software.
Here are some screenshots showing the resulting image after being processed by dscaler (note: I made the screenies before I got the original nintendo rgb cable, and I captured the pic while running the game in pal 50Hz modus. Ignore the blurry background, 'cause Star fox adventure uses some sort of depth blure to focus on the characters)
http://520050016814-0001.bei.t-online.de/tv1.jpghttp://520050016814-0001.bei.t-online.de/tv2.jpg