well I've updated it now a bit and used a bit more compression on images to achieve smaller size (but there really isn't any visual difference to them) and I've also upgraded Firefox to 3.6 which works little better now, so I think the problems are in browsers. My servers is pretty fast bandwidth wise since I can constantly down and upload at cca 550 kBps or more (I have a 5/5 Mbit line)
but I can't get it to work on Chrome, but there I also don't know how to update to latest flash. Sometimes even IE 8 just doesn't work ie. the first loading circle just keeps turning. But on firefox I find it great, works like a charm. But obviously it needs to take a few secs to load background, music, and then the images, but that's just a normal process not a server issue.