Screenshot on windows vista?

For some reason, every time I try to take a screenshot, it only takes a picture of the background desktop...

I'm trying to take a screen shot of the largest battle ever (over 10,000 soldiers) but I can't... :(

I'm Romanii and I sent 2 full stack armies after those annoying uber (2-3 silver chevron) rebel army that makes up the super rebels north of the alps.

btw, those uber rebels north of the alps are a GREAT addition. I was so happy because I actually lost 2 battles against them on medium with full stacks! XD

Just use fraps, its so much more convinient than having to alt-tab out and and paste into an image editing program.