Attempting to configure PHP 4.1.2 with command, 
./configure --with-mysql=/usr/local/mysql \
--with-xml --with-apache=/usr/local/apache \ 
--with-curl=/usr/local/curl \
--with-pspell=/usr/local/pspell \
--enable-shared-pdflib --enable-track-vars

where /usr/local/curl is a directory with properly 
installed curl 7.9.3.

when running  the above configure executable, error 
message is generated in "configuring extensions" section 
stating, 
checking for cURL greater than 7.8.1... ./configure: 
curl-config: command not found
configure:error: cURL version 7.8.1 or later is required 
to compile php with cURL support.

System has properly installed curl version 7.9.3 in 
/usr/local/curl