Try:

selector {
    -moz-border-radius: 3px;
    -webkit-border-radius: 3px;
    border-radius: 3px;
}

This will work in Firefox, Safari, Chrome and any other CSS3-compatible browser. It may be easier to make a separate class for this - there are 3 statements which are needed for full compatibility.

Also, try here (cssjuice.com) for some more techniques using images.

I'm not completely sure whether this will work with a table, but if you're in complete control - don't use a <table> for layout. Please.

(Note - I think its fine to use the table tag for tabular data, just not where DIVs should be used.)

Update: to apply to one corner only:

-moz-border-radius-topleft: 3px;
/* ... */
-webkit-border-top-left-radius: 3px;

Continue for topright or top-right.

You can do it like

border-radius: 5px 10px 15px 20px; /* This is a short hand syntax */

The above syntax works like a fan, starting from 5px and ends on 20px, just added a diagram below, the arrow in there depicts the start of the shorthand syntax flow.

Demo

To specify a particular radius, you can use property like

border-top-left-radius: 10px;

Which is equivalent to

border-radius: 10px 0 0 0;