Different thumbnail sizes depending on page

Hey Everyone. 2.5 looks great, I think I’m finally ready to make the switch to WP. I have a question concerning images though. I’m a graphic artist, and my website will mostly just be a portfolio, but set up as a blog (each project will be made as a post). And there will be a Home page that shows all posts, and then a websites, logos etc. which will really just be categories of posts.

In the posts, I want my images to show up as smaller thumbnails, and then when clicked, the full version is shown with some form of Lightbox. But my issue is with the thumbnails.

On my home page, there will be a sidebar type thing on the right, with a bio, links, etc. And the posts on the left, taking up like 70% of the main body. But on the category page, I want no sidebars. I want the posts to take up 100% of the body.

So my question is how do I have the thumbnails show up as two different sizes, depending on which page they are viewed. Say 400px wide on the home page, and then 600px when they are viewed on the category page. I know there is an option in the gallery to have two different sizes of thumbnails. But can both be used, and then dictate when each is used? Or I wouldnt mind just adding the images with normal code and not using the built in gallery, and just adding more code. Or a custom field or something.

Kind of complicated… But not so much. Just trying to be descriptive.

Any ideas? Thanks

EDIT: Like this http://www.chasewgraphics.com/images/wpdesign.jpg