It's not impossible, but Atomic Rocket Turtle doesn't have any packages for SuSE.
There are generally three ways to get Plesk and PHP 5:
* Install Plesk on a distribution that comes with PHP 5 (e.g. RHEL/CentOS 5, Fedora 4 or later, I don't know what version of SuSE)
* Install third-party PHP 5 packages for your distribution (e.g. ART for RHEL/CentOS/Fedora, dotdeb for Debian, ??? for SuSE)
* Compile your own PHP 5 packages if you know how to do this and not break Plesk (installing from source instead of installing packages will not work with Plesk)
I'm not too familiar with SuSE, but SuSE 9.3 has reached End of Life (April 2007) according to
http://en.opensuse.org/SUSE_Linux_Lifetime, so you might want to look into migrating to a supported OS and choosing one that comes with PHP 5 natively.