Where can I get <ldap.h> from? Do I have to install OpenLDAP or there is another way?
I would guess openldap2-devel package.
If you are lucky, you already have it installed in your system.
If not, I´ll suggest to use the header file contained in the openldap dev package, which happens to be (Open Suse 10.3):
There is no need to install the server.
Hope this helps.