If you build PHP 4.0.5 --with-imap-ssl=/usr/local/ssl, the build fails at least at my Slackware 7.1 and RedHat 6.2 machines :

Making all in imap
make[2]: Entering directory `/www/FAST/zooi/APACHE/php-4.0.5/ext/imap'
make[3]: Entering directory `/www/FAST/zooi/APACHE/php-4.0.5/ext/imap'
gcc  -I. -I/zooi/APACHE/php-4.0.5/ext/imap -I/zooi/APACHE/php-4.0.5/main -I/zooi/APACHE/php-4.0.5 -I/zooi/APACHE/apache_1.3.19/src/include -I/zooi/APACHE/apache_1.3.19/src/os/unix -I/zooi/APACHE/php-4.0.5/Zend -I/usr/local/ssl/include -I/usr/local/curl/include -I/usr/local/include -I/usr/local/include/freetype -I/zooi/APACHE/imap/c-client -I/usr/local/mysql/include/mysql -I/zooi/APACHE/swf/dist/include -I/zooi/APACHE/php-4.0.5/ext/xml/expat/xmltok -I/zooi/APACHE/php-4.0.5/ext/xml/expat/xmlparse -I/zooi/APACHE/php-4.0.5/TSRM  -DSUPPORT_UTF8 -DXML_BYTE_ORDER=12 -O -fomit-frame-pointer -march=pentiumpro -funroll-loops -malign-functions=4 -mwide-multiply -fschedule-insns2 -fexpensive-optimizations -Wall  -c php_imap.c && touch php_imap.lo
php_imap.c: In function `php_minit_imap':
php_imap.c:450: warning: implicit declaration of function `ssl_onceonlyinit'
php_imap.c:451: `auth_ssl' undeclared (first use in this function)
php_imap.c:451: (Each undeclared identifier is reported only once
php_imap.c:451: for each function it appears in.)
make[3]: *** [php_imap.lo] Error 1
make[3]: Leaving directory `/www/FAST/zooi/APACHE/php-4.0.5/ext/imap'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/www/FAST/zooi/APACHE/php-4.0.5/ext/imap'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/www/FAST/zooi/APACHE/php-4.0.5/ext'
make: *** [all-recursive] Error 1


If I remove the --with-imap-ssl, everything is building fine. If I build PHP 4.0.4pl1, it builds fine with --with-imap-ssl. 

-----------------------------------
OpenSSL 0.9.6a, static build :
./config --prefix=/usr/local/ssl
make
make install

IMAP-2000c :
make slx
mkdir lib
cp c-client/c-client.a ./lib/libc-client.a

PHP 4.0.5 :
./configure --with-apache=../apache_1.3.19 --enable-ftp --with-ttf --with-mysql=/usr/local/mysql --enable-safe-mode --enable-memory-limit --with-dbase --with-curl=/usr/local/curl --enable-track-vars --with-gd --with-jpeg-dir=/usr/local --enable-bcmath --enable-versioning --enable-trans-sid --with-imap=../imap --with-zlib --with-swf=../swf/dist/ --with-pdflib --with-xml --with-dom --with-wddx --with-openssl=/usr/local/ssl --with-imap-ssl=/usr/local/ssl --enable-sockets --enable-gd-imgstrttf


I haven't tested it with OpenSSL 0.9.6