As said in the title, my HDD puts out a clicking sound. Also when I close something that demands power etc all the icons for my programms take 2 - 3 seconds to appear. I assume my HDD is dying on me? If I bought another 500GB SATA and put my old HDD (the one currently in use) into RAID 1 (mirror effect), would this work as a decent way of backing up?

I would not suggest Raid for backup-- especially with a drive that is obviously failing. Mirrored drives often mirror the problems as well.
Drives can be bought fairly cheaply these days-- in stead of one monster 500 gig, why not 2 smaller drives... one primary and one for backups ?

Can't say I was aware that RAID mirrors problems, most are easily fixed though which still makes RAID appealing (to me anyway). The 500GB drive is needed, got a lot of music, games and films. I have a spare 160GB drive and was wondering how I would go about copying my internet settings etc as I'm clueless