Is Rockwell a web safe font?

As an alternative to Rockwell, you can use a font called Arvo from the Google Web Fonts API.

There's a very small set of web-safe fonts; Rockwell isn't one of them because it comes with third-party software like Microsoft Office.

That said, if you must use Rockwell as your primary font, be sure to define a decent font stack for it. That is, use CSS to define a list of fallbacks, where each fallback is a web-safe font:

body, input, textarea {
  font-family: Rockwell, "Courier New", Courier, Georgia,
                 Times, "Times New Roman", serif;
}

Some information on font stacks:

• http://www.petercolesdc.com/web-fonts-nice-honest/ (includes info on Rockwell)
• http://unitinteractive.com/blog/2008/06/26/better-css-font-stacks/

Nowadays (2011), modern browsers support embedding custom fonts via @font-face. Popular options include Typekit, Google Fonts, and Font Squirrel. Note that not all browsers support loading custom fonts via CSS, so you should still list web-safe fonts as fallbacks.