Hi there.
Is it a silly question, or is it totally impossible.
Nothing is impossible... However, upgrading SME 6 to Apache 2 to is going to result in ALOT of breakage. My best suggestion would be to start working google, looking for RH 7.3 Apache 2 rpms (httpd). Install them and start fixing the breakage.
However, I can't imagine what would motivate you to do such a thing to SME. You are going to have to spend hours and hours fixing things. Alot of that makes SME what it is is highly dependent on apache. You are going to have to rewrite ALL (or many) of the httpd.conf template fragments, and that's just the beginning.
Greg Zartman