Different hyperlink properties in posts & sidebars? Possible?

I am working with WP 1.5 and attempting to develop some facility with the whole CSS thing.

My challenge is this: I would like to use different text attributes for the “a” selector in the sidebar and on the main page. I would like for hyperlinks to be underlined in the posts, but I don’t want them to be underlined in the sidebar.

I’m still trying to figure out the difference between class and ID selectors, and I think this is where I need to go, but I’m not sure

FWIW, the site I’m working on is https://www.budmandotcom.com