I too am having great problems getting PHP to install with dom support.
I have tried both 2.2.11 and 2.3.3 of libxml and I still get the same checking for libxml version.. configure: error: libxml version 2.2.7 or greater required when I go to configure. I have removed 1.* versions of libxml from my SUSE 7.0 box and still no luck. I have reinstalled libxml with both of the above versions.
Anybody?