I had a feeling you might have an issue. As diggingdeeper points out; there is no sync. You need a VGA to RGsB lead (Gs indicates the sync is on the green signal), plus you need a SCART block that is wired for RGB - any old SCART block won't work.
If you fancy doing it yourself, the circuit to do so is here: http://www.epanorama.net/circuits/sync_r.html
(usual at own risk disclaimer
Alternately, Avermedia's KeyLite (aka AVerKey Lite) will do resolutions "upto 1024x768". There is a used one on ebay for £20+p&p, or Maplin.co.uk have them new for £50 (stock code A30AU).