First off if you don't want to see spoilers get out.

Moving on i'm doing the quest called finding the garden of edan.  

The part i'm stuck on is where to find the G.E.C.K.    

I know your suppossed to find the Fawkes mutant and ask his help but i stupidly killed him and now don't know how to get it, i went into the rad infested hallways thinking it might be there but couldn't find it.  

And i don't have any saves that are even close to that point in the game.  So any help on this matter would be appreciated.

thanks.

If you've killed Fawkes, you're pretty stuffed.
AFAIK, Fawkes is the only char able to take the rads to get the device.

edit: maybe this can help you, I haven't confirmed the method myself though

http://www.gamespot.com/xbox360/rpg/fallout3/show_msgs.php?topic_id=m-1-46562731&pid=939933

Well i found it and it was easy to get...the easiest things are always the hardest for me to find in games for some reason...like when i was stuck in a part in mirrors edge for 2 hours and all i had to do was walk up to a truck. thanks for the help though.

You have to put on that super radioactive suit from that room which you have to unlock and take heaps of rad-x and rad away and then run through that radioactive room and quickly get it