Change teaser with Content Template?

Hi, I 'm writing articles on my blog & would like to change the look and feel of my teasers. The teaser publishes the first 600 characters of my article. It would be nice to change the type to another font, or change the first paragraph into regular on the teaser page (but remain bold in the article itself). I thought I could do that by installing the content template, but I don't know which template variables I have to use. Anyone any ideas?
PS: using drupal6