Problem with PC...need help

hi guys
i have a P-III 933 Mhz compaq pc
nowadays when i try playin games etc on it …there is a problem…i kno my hardware may not support these high resolution games.

in one game…hitman II…it said that the color depth is not enough…i have max 24 bit true color on my pc

if i get a video acc card…somethng like Nvidia…or GEforce…will that solve the problem

or Is the problem of color depth also associated with the monitor…

what is the root of the problem and how to rectify it…

I think the installed gfx card is just too eak and obsolete for actual games.
If you would replace it, the next thing would be a faster processor (maybe also mb) and more RAM…