Hardware & network for e-commerce site

I want to set a web site to sell my products online. Does anybody have
suggestions of a good network configuration and any recommendations of
Hardware that would be appropriate? Am not interested in using any of
the prepackaged and expensive hosted solutions (Yahoo, etc...). I just
want to do it by myself.

I was initially planning to use 4 computers (user machines excluded):

- A webserver running Linux/Apache/php/mySQL/FTP
- A firewall box (most likely running IPtables)
- A file/printer server (mostly for internal use like order printing)
- Potentially a mail server

As far as the H/W is concerned, I got different opinions: One friend
recommended me to buy a very cheap power-efficient computer with good
memory for the webserver since it will be online 24h/7. Like a P3 Dell
Optiplex 500Mhz (not sure if this model is that power efficient) or
even an old IBM P3 Thinkpad laptop. Another friend recommended instead
best of breed equipment for reliability purposes. Not sure for the
other boxes.

Thanks for the help,
Nkol

PS: If anybody knows a good book about this subject, that would help
too.