Here's a care sheet for you:
http://reptiles.thepsionguild.net/ga...caresheet.html
I kept a wild-caught adult female Eastern garter when I was younger. I had her feeding on f/t fuzzy rats on the second try. She had no problem at all with eating rodents. Never had to scent after she ate the first one.
Some advice--earthworms are great for scenting over garters to take rodents. Just rub some worm slime on the mouse.
Reduce the amount of scenting if the snake doesn't take an unscented mouse on the next feeding. Some garters will take to it almost immediately, some will take a little longer, but I've never had a garter (and I've kept at least 5) that I couldn't scent over to rodents.
Don't give them live rodents, of course.