I hope Im not ruining this for anyone, but yes, no matter how you die, you turn in to a zombie. The virus is in everyone. Thats why when Shane snapped Randalls neck, he came back, and thats why Shane came back too. It seems like in the show they are just skipping straight over this stuff..the comic covers it though. They saw it with the 2 security guards, and now with Randall and Shane.
Cant wait to see the finale, the show has been going off a little, they need to make it up in the finale.