It depends on a few things you haven't listed. For starters (just looking at it) not much.
What is your P4 at STOCK speeds, no overclocking. What chip/core?
What speed is your RAM? PC3200, 4000, what? And is it a single stick, 2 sticks?
What motherboard?
What kind of shape is it in? How old is it?
Older CPU from what I can tell, probably an older motherboard to match. I'm going to assume PC3200 single stick. Again an older video card (btw is it 128MB?) with a very small/generic power supply that probably came with the case.
If it comes with the LCD you'll get more, but honestly I wouldn't pay more than $400 for it. It won't run any new games decently, there isn't much that's desirable besides the DVD/RW and the LCD.