No need for system specs. To get this resolution simly go open your steam, Open up your games collection, right click on Counter strike source, then click properties, then launch options.
Then you type -w 1280 -h 1024
Then click apply and open the game and it shud be that resolution.
Remember to do this when your not in game. the lauch options is a command line for what the game shall start whit of settings. so when you type in the above you will tell the game to start whit that ressolution.
If that dosent work i recomend trying another driver