Error Loading OeratingSystem .... HELP!!!

Hey

We need help!

at some point something happened to our hard drive, and we get the Error loading opearting system, during the boot process. Now we got the computer (dell desk top), from my wifes grandmother,she said it  has had issues in the past, but what the hey, we're poor and to get a computer for free was a good deal for us.  Anyway, we use(d) it alot storing all of our wedding pictures, or little boys first two years of baby / toddler pictures in there and without warning we get the error and suddenly, by all accounts we have lost everything. a very sad state of affairs.  Now I'mhoping worst case scenario we can take it to a repair stor and they can retrieve the pictures and we can get the stored on to CD's for printing and placement on to another computer when we can afford it. 

I'm ok with computers but I have no idea how to try to fix this one, I kow if we reboot we will definately lose everything for good. So then maybe we can repair ..... HOWEVER, the computer was purchased  and ran with windows ME, but was upgraded to XP before we were given it. So where to go, if I try and repair with the Windows ME disk, we will lose everything, and as the XP disk is only an upgrade disk, then that is not going to repair anything.

Does any one know of any method of repair ?????