You can change the icon and font size in Windows XP and probably Vista with the Display Properties menu Appearance tab. Click the advanced button and then click the drop down menu and choose Icon. You can change the Icon pixel count as large or as small as you like. Give it a whirl and you'll see what I mean The task bar will get thinner when you increase the screen resolution, but I don’t think you can do anything about that.

http://img.photobucket.com/albums/v65/ewescoat/comparrison.png

I have cataracts in both of my eyes, so I set most of the Windows background color to black and most of the font color to white so I can look at the monitor and not be blinded by the light. I have also raised the size of the Icons a bit so I can still see them. My current screen resolution is 1280X1024 and the Icon size is 72 at its' largest and smallest is 16. My current Icon size is 40 and is not displayed in the picture.