Running PHP 5 and PHP 4

[T^2]

I'm just wondering if anybody has had any problems with running PHP5 and PHP4 in parallel using any methods (I know of two: proxy and another one without a proxy)?

Like does it create a lot of stress on CPU, Ram or causes any instabilities.

Thanks,

Tang

[fireshark]

The method I knew was PHP4 as module, PHP5 as CGI and mime to .php5 files only