Select all 'tr' except the first one

sounds like the 'first line' you're talking of is your table-header - so you realy should think of using thead and tbody in your markup (click here) which would result in 'better' markup (semantically correct, useful for things like screenreaders) and easier, cross-browser-friendly possibilitys for css-selection (table thead ... { ... })

ideal solution but not supported in IE

tr:not(:first-child) {css}

second solution would be to style all tr's and then override with css for first-child:

tr {css}
tr:first-child {override css above}

By adding a class to either the first tr or the subsequent trs. There is no crossbrowser way of selecting the rows you want with CSS alone.

However, if you don't care about Internet Explorer 6, 7 or 8:

tr:not(:first-child) {
    color: red;
}

I'm surprised nobody mentioned the use of sibling combinators, which are supported by IE7 and later:

tr + tr /* CSS2, adjacent sibling */
tr ~ tr /* CSS3, general sibling */

They both function in exactly the same way (in the context of HTML tables anyway) as:

tr:not(:first-child)