Capturing screen in Samsung Galaxy ace is so simple and achive this without using any third party application. To work this trick OS version Should be Android 2.3 GingerBread. If your OS version is 2.2 then upgrade it free.. if you have allready 2.3 then try it.
1. First press and hold the backbutton in your phone.
(marked in picure as 1)
2. Now Click your Home button and relese....
(marked in picture as 2)
If you here a capture sound and see a capture transition..Done...!!!
Now Goto your SD Card using any File browser ...will get a folder named "ScreenCapture" containing captured picture.
below is the picture captured using my Galaxy Ace GT-S5830 Android 2.3.4 GingerBread
I am tested it with Galaxy ace v 2.3.4 and worked for me.
If this helped you please do a comment....if know any other way please share by comment.