That's quite interesting ... I also found this: http://wiki.macromates.com/Howtos/Requests
But with this approach, only TM will look for MAMP's PHP ... if I want my Terminal to use MAMP's PHP also then changing the .profile file is necessary too.
Thanx again for the tips :-)
How to config the internal TM preview browser to run the MAMP PHP engine?
TextMate respects the TM_PHP environment variable if it is set. In TM's preferences, choose Advanced > Shell Variables, and add TM_PHP with the full path to the php binary (in your case, probably something like /Applications/MAMP.app/Contents/Resources/bin/php (total guess, I've never used a mamp before)).