I have Windows XP Home Edition.
Whenever my web browser window is maximized, the taskbar is not visible at the bottom of the screen. I right clicked on the taskbar and "Lock Taskbar" is checked.
Why is it still not showing?
Is the browser running in full screen mode? If so try hitting the F11 key.
You mean the window your viewing is enlarged to cover the taskbar?
If so, you need to see what the window properties are set to for your browser and it may be that some site you visited has set up a new default overidin your settings. I have come across several sites in as many years that have completely screwed up my preferences for viewing.
Right click task bar > properties > On Taskbar appearance, check "Keep taskbar on top of other windows".