Ok so my MacBook just died (right after my new battery and stuff had arrived grrrr). Anyway I found an identical one on eBay and bought it. Now my question is can I take my old hdd and put it in the new identical mac and have my system back?
Depends on what the issue was with the previous one. Can you mention any symptoms it showed when it died? If it was an issue with the hard drive obviously there is a chance of data loss even with a new machine.
As long as your HD from the previous MacBook did not fail, you can swap it out and have your old system.
Here is a great resource on how to repair you MacBook. http://www.ifixit.com/Device/MacBook Select the correct model and then chose hard drive replacement. It will give you step by step instructions.
I believe it was my graphics card that died. The hard drive is fairly new (replaced). I could turn it on and after boot time I could hit the caps lock button and it would turn on. Just no display. Even checked to see if it was just the backlight but nothing at all.