If you really want to use tabs (== tabulator characters), you have to go with the following solution, which I don't recommend:
<pre>
test
	test
		test
</pre>
or replace the <pre/>
with <div style="white-space: pre" />
to achieve the same effect as with the pre element. You can even enter a literal tab character instead of the escaped 	
.
I don't recommend it for most usages, because it is not really semantic, that is, from viewing the HTML source a program cannot deduce any useful information (like, e.g., "this is a heading" or such). You'd be better off using one of the nice margin-left
examples of the other answers. However, if you'd like to display some stuff like source code or the such, the above solution would do it.
Cheers,