Change my theme to single column when viewing single photos

I’m currently using the Gallery software for my photo gallery on my WordPress blog. It’s nice, but since WordPress now has a pretty cool media library I’m thinking about starting to post my photos straight to WordPress (and stop using Gallery). But the content area in my current theme is pretty narrow and I would like to display big photos when people click one of the photos in the gallery.

Is there a way I can change the theme to a single column (wider) when viewing single photos (attachments)?
– maybe I can add some PHP code to my template that checks if category=gallery and then it loads a different CSS style (or adds a different CSS class to the content area) to make it one column (not load the sidebar)?

If you want an example of what I’m looking for you can take a look at Matt Mullenweg’s gallery: https://ma.tt/2008/09/day-in-davao/
and how he displays single photos: https://ma.tt/2008/09/day-in-davao/mcm_8841/

Any help appreciated ??

– Hannes