I often hear website owners in forums etc. asking if using PHP, ASP or any other server side scripting language can hinder the effectiveness of sites from an SEO standpoint. The answer is no, but here's a little more information.
PHP and ASP are very popular server side scripting languages. There are others such as Pearl, Python and Cold Fusion but PHP and ASP seem to be more common. Server side scripting languages are often used in conjunction with a database such as MySQL. In essence the scripts grab information from the database and create web pages on the fly to display to website visitors and search engine crawlers.
This method of creating web pages allows for many web pages to be easily created and managed and is used by popular systems such as Wordpress and Joomla.
The concern some people have is they believe HTML pages are more effective when it comes to being found and indexed by search engines. This is wrong. When a server side script creates a web page the resulting web page is HTML in just the same way a static HTML page is HTML. Web browsers read and understand HTML and that's what server side scripts send to them.
It is fair to say that some scripts create 'messy' HTML but it's still HTML nonetheless and systems using server side scripts offer many advantages over simple static HTML pages.