Gallery/portfolio in a post with one example image

I’ve been using MODx for most of my websites but recently i’ve been trying WordPress, so i’m a newbie here.

I want to have a gallery in a post which only displays one example image if you view the post on the homepage and displays the whole gallery if you view the post itself.

Maybe there’s a plugin or a hack to acomplish this, I can’t seem to find a way but scripting a plugin myself…

Thanks!