I'm running on Mac OS X 10.4.11 (Tiger) Server and ran into the same SSL issues you're describing.
On Tiger Server there's an /etc/certificates directory that an x509anchors.pem file. I initially tried to set SSL_CERT_DIR to /etc/certificates, but kept getting the "http.rb:590:in `connect': certificate verify failed (OpenSSL::SSL::SSLError)" error. Eventually I figured out that you actually can specify the file directly, as follows:
export SSL_CERT_FILE=/etc/certificates/x509anchors.pem
If you're using /etc/s3conf/s3config.yml, like I am, then you can put the following in there:
ssl_cert_file: /etc/certificates/x509anchors.pem
I haven't played with Leopard Server enough to know where the x509 file(s) might be on there and /etc/certificates/x509anchors.pem doesn't seem to exist on Tiger client. So in those cases, you might need to do it the traditional way.