Installing a secondary HDD

I'm down to 700MB on my primary 80GB HDD, so I went out and bought a secondary drive...

The prick at the store flat-out refused to install it for me though, so I'm stuck. I could wait for the end of the weekend to get it installed professionally, but I've just got DSL so I'm pretty anxious to start downloading things.

Can someone guide me through this? I know virtually next to nothing when it comes to hardware, and every site I've been to hasn't dumbed it down enough for me to understand.

>>2

Already done, most of the files I have are work-related so I can't easily remove them.

>>3

The cable I was given doesn't fit in the back of the HDD... I think I'm just going to have to wait for a friend to help me out sometime next week, I can't tell what I'm doing. Thanks anyway.