"Couldn't load c:/php/php5apache2.dll into server"

But the path is correct 100 times! I did everything like it said in install.txt of PHP archive, but it doesn't work. I tried to install php like cgi binary, but it also didn't work. BUT. PHP4 installed without problems. What am I doing wrong or what should be done else?

the error doesn't indicate that it can't find it. it indicates it can't load it.
Did you use the same compiler as you used for apache to compilek the dll ?

Which version of php are you using?
which version of apache are you using?
post your httpd.conf (and sourced files)

I seem to remember there were some compatibility isues with php5 and apache. Do check that the versions of both are compatible with each other.