I use CSS and HTML and have basically designed the sites I am responsible for for 1028px width and they look ok on smaller resolution screens but poor on higher resolution screens - I suspect that this is because I use mainly fixed widths and px sizing and suspect I need to use % and ems to make it 'scale up' - anyone got a link to a tutorial or dicsussion on bes practise

you should always try and use % and em. fixed widths are okay but fonts should always be in em.

you can go to w3schools. they have good tutorials on there that follows strict web standards.

Even you used fixed widths, you should have all the tags within the container to make it center for higher resolutions without losing their original quality.