In case anybody has trouble configuring PHP with LDAP support on a Solaris 10 box, here is the configure line I used:
./configure --with-nsapi=/opt/SUNWwbsvr --enable-libgcc --disable-libxml --with-ldap=/usr/local --prefix=/opt/php/php-5.0.4
The important part to note is the location used for --with-ldap= ; which for most S10 people, will be "--with-ldap=/usr/local".