developing a small images preload plugin

I am looking into a developing a small plugin that will preload images that the top post of the current page is linking to. Meaning, that if the first post in the page has links to images, I will preload them.

For this I figured I will parse the content of the topmost post and build a small javascript script to preload them. I need to put this in the header, so I need to get the content of the topmost post in the header. I know I can do this by using have_posts() and the_post() like the Loop, but then I will lose the first post because, as I understand, the_post() advances a global counter or something like that.

So how can I get the content of the topmost post while still in the header? I don’t need to modify it, just parse it.

Thanks