Hi, Kim. I haven't tried it, but according to this post, here's the scoop:

The index.php file they're referring to is the one in your currently active theme folder, which is /wp-content/themes/yourthemename/.

Note that depending on how your theme is structured, this may not have the reversing effect on all kinds of pages of your blog. It should reverse the order on your home page, assuming that you're not showing a static page on your home page. But if you want the same effect on your categories, archives, or tags pages, you may have to make the same change in other files in your theme.

Hope this helps.

Steve

It's the posts I want in reverse order. I'm going to try it in a few minutes,thanks.
Kim

Edit:
Thanks Steve, I did it and it worked.
Its the wordpress site about my kidney listed in my sig,and making it reverse the post order makes it read a lot more coherently.
Kim