There are all kinds of companies willing to do whatever they can, but it might cost you a lot.
And there's a lot of do-it-yourself-software, like from http://www.ontrack.com. I never used it, so I don't have any recommandation.
Searching these forums or google for "data recovery" will learn you much more (including sponsored links on google).
And just an educational remark: you risk to lose whatever you don't backup on another medium. That's one the better things to do with a cd- or dvd-burner. But it might be too late now.
All my data has disappeared on my D Drive (no idea as to how this has happened)This is where I keep most of my important data because I thought it was safer than the C Drive.
I have Windows XP
Is there any way that I can retrieve this data?
Any ideas as to what can have happened to it?