Cascading Style Sheets are implemented in all current browsers. No browser is 100% compliant yet, but for basic text display all 4X and later browsers will respond the the basic CSS text display properties.

The Font tag will let you create some of the same display effects, but as of HTML 4.0, it is no longer considered a valid tag. It is a good idea to begin using CSS to ensure your documents will be compliant in the future as well as today.

For a full reference and tutorials on CSS, check out The CSS Zone. This chart provides a few highlights:

Inline structure: <tagname style="css-property: value; css-property2: value;"> Declaration structure, used between style tags in header of document or in external .css file: tagname {css-property: value; css-property2: value;}
set text color	color: colorvalue;
set font family	font-family: 'font name', 'font name2', generic;
set text size	font-size: XXpt;
set bold	font-weight: bold;
set normal weight	font-weight: normal;
set italic	font-style: italic;
set normal style	font-style: normal;
set alignment	text-align: left/right/center/justify;
set underlined	text-decoration: underline;
set underline off	text-decoration: none;

Use CSS rather than the font tag to set font display values.