I installed PHP 5.4.9 on Debian Squeeze and it resulted with imscp-autoinstall giving the error that php5-suhosin couldn't be installed an thus fails.
What i did was that i removed all code inside autoinstaller::Adapter::Debian::installPackages and it let me through although suhosin wasn't installed.
And everything seems fine, haven't found any problems yet so.
I think there should be some kind of check which php version is installed before throwing an error.