Funny, the default XP theme always makes a screen feel much more crowded than using a Mac, but maybe that's just taste. Taking web browsers as an example, Safari has a zero pixel border on the left and a thrifty 15 pixel scrollbar on the right; the buttons at the top are far smaller than the IE default, and the bottom strip can be turned off entirely. The only universally lost space is the stripe at the top for the menus, which is smaller than the default Windows Taskbar, and though you can't hide it you don't need the menus at the top of every window which saves net space.
Still, the obvious things to do are:
-Reduce the size of the dock; either use the pref pane or just drag the seperator over by the trash
-Auto-hide the dock (again, right/control click on the seperator or use the prefs; it pops back up when you put your mouse on that screen edge)
-Move the Dock to either the right or left side (it makes more difference on widescreen monitors, but is still a bit more efficient on standard 4:3 ones like yours)
-Use the Finder View Options to reduce icon and font size
-If you don't like or use the left bar in Finder windows, it can be hidden (or shrunk) by dragging the seperator
-You can switch to non-metal Finder windows to save the border space, though you loose the convienent top buttons
-While web browsing, you can reduce the font size temporarily (as said, by using command-+ or add the buttons to the top toolbar), or permenantly (check the prefs--default to any font size you like)
-Finally, if you download the free Tinkertool, it lets you tweak a few more visual things that might get the interface looking more to your taste
