Well, as far as I know, the programming language used for the website does not effect the rankings of website in search engines and the most important thing to get good rankings is content. If the content of your website is good, you will definitely get good rankings and building backlinks will be easier for you which will help you to get good rankings in search engines and more PR for your website which is also important in terms of Google which is considered to be the best search engine

Hence, you can build your website in any programming language of your choice, however, when it comes to sitemap of your website, you can make it in XHTML which would be a better option.

The spiders have absolutely no problem reading PHP as after all it is just a bit of scripting. The problems come when you make the pages unspiderable with lots of dynamic query strings in the URL.
Have a look at the stuff here highrankings . com and all your questions will be answered.