There is a program called 'ghost' which enables drives to be mirrored, and I know there is a lot on this forum about how to install a new drive. Try searching for 'new drive' and 'ghost'. I think Norton do it, but I have a basic programme which will run in DOS if you need (610k). Most new drives come with software to enable drives to be 'mirrored' old to new. Of course, if the failing drive is your C drive it gets more complicated, I think, but one of the experts will have a way to do it I'm sure.
If you have a spare drive plug in your 'pooter (I believe you can have a total of 4 including CDRoms/DVDRoms) it will make life much easier.
Might be best NOT to switch off until that new drive has winged its way to you!!
Good luck!