This is a great MOD, My wife had been trying to get me to do this for weeks, last night I finally did it
My Daughter made the graphic not bad for a 15 year old. its amazing what kids can do.
I am using X-Cart version 4.0.14 and found a few things different than above.
8. edit skin1/admin/modules/Gift_Certificates/gc_admin.tpl
on my cart it is at skin1/modules/Gift_Certificates/gc_admin.tpl
2. Copy the graphic to files/images/misc/giftcert.jpg
dirs had to be created ( I didnt have the images or misc directories in my shopping cart ), I didnt know if they were in the version you used when you posted.
Not counting the graphic the whole mod took about 10 mins, then aligning the names and such took about 20 mins. Make sure you print them out because it looks a tad different on the paper than on the screen.
Putting the code in the email I still need to play with a little so my customers can find a easy way to print out the cert with out all the other information that comes in the email.
Again Awsum job