php4 vs php5 vs asp
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 |