Sharp images from EOS 20D (1 Viewer)

I've been using a 300D for some time and have managed to obtain some excellent images ( see my gallery ) but I' now upgraded to the 20D and I am experiencing some difficulties.
1 The images don't appear sharp in the L.C.D. monitor but I've read a couple of reviews that put this down to fact that the zoom control is magnifying the images to much at full zoom causing the images to appear unsharp.
2. when I load the images onto my P.C. they also appear not to be sharp.My monitor runs at 800 x 600 pixels,if I increase the resolution to 1280 x 1024 the images become pin sharp. When I print the images at A3 they are sharp so it does' appear to be a camera problem perhaps a monitor problem. If I run the monitor at the higher settings all the photoshop menu and icons are too small to read. Do I need a new monitor. The existing monitor is only 12 months old. Any help,suggestions or ideas appreciared.
Malcolm

Malcolm,I have found that my images with the 20D are not as sharp as the ones from the 300D,perhaps I have altered settings,or should have left some on the default.If anyone using the 20D could possibly say which settings they are using in general ,it may help.

Malcolm, it seems what you feel you’ve lost is an ability to assess how sharp your original pictures are when the complete pictures are viewed in Photoshop (perhaps using “Fit on Screen”) and with the monitor set at 800x600 resolution. You may find a specialist picture browser/displayer makes a better job of displaying pictures. The freebie here does good quality resampling with minimal jaggies (double click on a thumbnail for full screen) :
http://11view.stratopoint.com/