Can i play just cause on pentium 4

http://www.systemrequirementslab.com/cyri

run this scan and it will say what can run on your PC and what not

Pentium 4 are you kidding me?

Just Cause 1? Sure.

Just Cause 2? Doubt it.

Yes, you can play a lot of titles on the pentium 4 still. Don't let people tell you otherwise, as I have a machine with a P4 and a Radeon 4650 and am even able to play new titles (2012). In fact, intel have decided to re-introduce hyper threading after many years, since it was incredibly effective in the Pentium 4 architecture.

Examples of games you can play at 1280 x 960 (Fully Maxed or mix between Max/Medium no AA):

Just Cause/Just Cause 2
The Witcher Enhanced
Skyrim
Most crappy "indipendent" flash platformers (i.e. Isaac, they bleed pixels etc)
Far Cry 2
Fallout 3/New Vegas

and much much more.