after mod rewrite, using disallow .php in robots.txt

is it a good idea?

[sirkei]

Hi all,

i used mod rewrite for my website and i heard that if i write one disallow .php line in the robots.txt file then it is better for spiders to crawl deeper into my site and thus getting better placement in SE. but my website has one forum and boards using php feature. So if i use disallow php, will this affect spider crawling to my forum and thus getting no PR?