Hi. I have this too: I'm running CentOS 4.1, 64-bit.
The first error I got was unable to link with libmysqlclient. I think
I fixed this by installing mysql-devel but I may also have edited the lib path to /usr/lib64 as well. I can't remember so I'll have to report back on this when I next install on a clean system.
The second error:
/root/ispconfig/openssl/lib/libssl.a(s2_srvr.o): relocation R_X86_64_32S against `ssl2_accept' can not be used when making a shared object; recompile with -fPIC
was solved by removing reference to the ISPConfig-supplied openssl. This may be an issue with the compile options for the ispconfig-supplied openssl, but if openssl is supplied with the distro, I see no need to recompile it.
Either way, 'srg' got it right by editing compile_aps/compile and changing the PHP
directive "--with-openssl=$(INSTALL_ROOT)/openssl" to "--with-openssl"
I do have openssl-devel installed in case you need this.