I have compiled and installed python 2.5.1 from source on FC4 64bit and have compiled mod_python however before I run make_install I wondered has anyone done this and does anything break in Plesk?
You have to install new python separately in different directory than original python (because original is used by yum/rpm) and then recompile mod_python with new python path.
Yes, you don't want to overwrite the existing python with 2.5. It will break a great many things, since the vast majority of internal configuration tools are python based.