Looking for some [freeware/opensource] tool in order to make it easy to profile a big php project on win32 platform. Need to find out which part of code is most time consuming.
Yes, use XDebug, and once you're in it, use this technique, which works on any platform.
Don't think of it as measuring time.
Think of it as trying to ask, predominantly, What is it doing, and Why is it doing it?
xdebug works quite well http://xdebug.org
Also wincachegrind is a good tool for looking through the profiler's output. http://sourceforge.net/projects/wincachegrind/
As well as (if the profile file is small) webgrind http://code.google.com/p/webgrind/
You'll want to install and configure Xdebug. It's sort of the de-facto standard PHP debugging and profiling tool.
WinCacheGrind can crunch the profiling output. It's a bit buggy, but it does the job.
In addition to the excellent xdebug (as mentioned by others), you can also look at xhprof.