Depends completely on your application. A neat setup for a web based app is to have 2..n servers sitting behind a L4 switch for load balancing. The servers need not be amazingly gruny beasts, which is where the beauty lies.. You just add low cost machines when you start to lag at the front end.
If then you need a database, open a nice fat channel from the web servers to a dedicated (suitably tuned) database server on a private network.
Not specifically answering your question, but perhaps a viable alternative?
Are you posting in the right place? Check out Where do I post X? to know for sure.
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
Want more info? How to link
or How to display code and escape characters
are good places to start.