SCART is just a plastic connector. VGA is a whole signal level/timing spec. You can't convert one to the other
Assuming the SCART is a standard video signal (PAL or NTSC), conversion to VGA (say 640x480 or 1024x768 etc) requires a frame buffer. You have to digitise the video signal into a bit of memory, one frame at a time, and then resample the frame buffer into the desired output resolution. The frame rates will be different at the two ends... a very tricky piece of hardware.
Many years ago a box which did this would be £10,000 but now they are dirt cheap. I bought one on Ebay recently which goes the other way round (VGA to PAL), called Grand Ultimate XP Pro PC-TV Converter, about £50. I don't know if this does the sound also but I believe it does. I am sure there are others which go in the direction required here.