Just received mine today(thanks oregonarcade!), including unpacking it, taking pictures of how the original was set up(just in case), removing the old and installing the new, I had it fired up and playing in less than 30 minutes.
Before anything, I made sure my power switch on the back of the machine was off, and the game was unplugged from the surge protector.
You need to find out what color board is in his, if it's a green or red board. Then he will need to find a paired hard drive and board of the same color board he has. Then it's remove 5 screws(flat head) on the edges of the board, four screws(flat head) on the hd, unplug what needs to be unplugged from the old(make sure to remember what went where) and place the new. If you need help, I took pictures of how mine was set up before I disconnected anything, so if you get lost and need the pics, let me know. I think there were 6 various plugs on the board and two on the hd you have to switch over.
Keep me updated on how it goes.