Installing external drive as as a second internal hard drive

[Shamanuk]

Hello

I have mint13 xfce version.
I have since 2009 had a seagate 1tb external hardrive in the last few months it has connected and disconnected.
The intervals of how long have been getting shorter and shorter, last night it was only 2 minutes.
I am certain the hardrive is not dead just the case. So I have cracked the case open and have been lookijng at how to make it a second hardrive.
Now I have on this particulat drive over 700gb of data I do not want to loose, I have been reading yp how to do this but of course eveeywhere I have been looking has refered of how to do this with windows.
Has anyone done this and give me some advice?