Individual Post Template Based On Category Possible?

since i found the wonderful world of “page templates” (ability to create seperate templates for each page in wordpress) i have a problem i can’t figure out.

i am having trouble trying to find out how to do that for posts based on the category it’s in. i would like to have a different layout for each post depending on the category it’s assigned to.

my template doesn’t have a ‘single.php’ but uses the ‘index.php’ instead to display the posts.

it doesn’t seem to be as easy as creating a ‘page.php’ page and renaming it and selecting it in the admin.

thanks!