Disable CSS Output Selectively

I've got a few forms that look terrible when Output CSS is turned off and great when turned on, and a single form that looks terrible when Output CSS is turned on and great when turned off. Unfortunately I don't seem able to target the one form via Firebug when it's looking bad - FB just doesn't seem to work at that time.

The site is http://www.horizonsforhomelesschildren.org/ and the one form that works properly with Output CSS set to No is the newsletter sign up in the header. Other forms, for example this one I'm developing now at http://www.horizonsforhomelesschildren.org/understanding-homelessness/policy-advocacy/photopetition/ look pretty bad with Output CSS set to No and cleans up beautifully when I set Output CSS to Yes. The newsletter form issue is that the items line up vertically and not horizontally with the setting on Yes.

Is there a way to set Output CSS to Yes but override that setting or otherwise resolve my issue with the newsletter sign up form in the header?

Thanks for your thoughts.

Chris, your suggested reading is intriguing - thanks! I think it's close to what I need, but seems to turn off CSS on a whole post or page based on the various options. My issue with this is that the form I need to turn CSS off for is in the header, so it actually needs to be disabled for that particular form but remain on for other forms which may appear on the same page. Do you know of a way to specify a particular form to turn off CSS output for while leaving it on for others that may appear on the same page?