Just Cause 2 for Windows XP

[iou]

Just Cause 2 does not support Windows XP.

Afaik there is no XP hack out yet, there might be one soon, who knows.

So for now, either get Vista/Seven or wait.

It's Windows XP that doesn't support DirectX 10.
Just Cause 2 does not support DirectX 9, aka it's DirectX 10 only.
They did make a crack so that you could use DirectX 10 on Crysis playing on WinXP, so it's possible indeed.