The effect attribute is proprietary for the WebTV/MSNTV browser, so pages tat use it will not validate
There are 3 values that you can use for
effect="?":
emboss, shadow & relief.
Here is what they look like. I'm using a dark gray to show them against my black background.
<font effect="emboss">emboss</font>
looks like: emboss
<font effect="shadow">shadow</font>
looks like: shadow
<font effect="relief">relief</font>
looks like relief
Also, see MrsK's page on font effects for her perspective. She likes to match the font color to the bgcolor.
Happy coding!
Gnubee