For every client (Browser, Spider, Bot, ...) PHP is not existent. All they see is a HTML file. So most searchengines will in fact crawl through your site just fine.
However there are a few things to keep in mind:
- some searchengines do not index pages that end up in .php. Don't ask me why, they just do.
- some (in fact MOST) searchengines do not index pages that look "dynamic". For example if you add a parameter to your page like
index.php?page=homepage
or
index.php?page=news
to display different things you might end up screwed. Searchengines don't like dynamic content and therefore they tend not to index it. A possible workaround (apache only) can be found on www.biochronox.com in the php codes section (licensed GPL).
Also do not forget to add appropriate META tags to your headers. There are many websites out there that describe the problematic much better than I can.
Hope this helped a bit,
Dominique