the comparison says it all. from (http://otn.oracle.com/pub/articles/hull_asp.html )
Table 1

 
PHP 4
PHP 5
ASP.NET

Software price
free
free
free

Platform price
free
free
$$

Speed
strong
strong
weak

Efficiency
strong
strong
weak

Security
strong
strong
strong

Platform
strong
strong
weak (IIS only)

Platform
any
any
win32 (IIS only)

Source available
yes
yes
no

Exceptions
no
yes
yes

OOP
weak
strong
strong