Server to Handle 700 Users Online on a single phpBB forum. Thats the only thing on the server will be hosted with a default phpBB install.

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ANSWER
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Get a dual processor or dual core server with fast disks and 2GB RAM would be a plus. Don’t bother with a control panel and look into going 64 bit if possible. Install lighttpd – http://lighttpd.net with FastCGI & PHP.

Compile xcache into PHP

http://trac.lighttpd.net/xcache/

It works well with lighttpd & fastcgi and is comparable to eAccelerator, APC, etc.

Run MySQL 5 with a tuned configuration.

Use tuning-primer to assist with tuning your my.cnf;

http://forge.mysql.com/projects/view.php?id=44

🙂