PHP won't start

I had an 8.1 box with apache running happily. I just installed the PHP packages, and now apache won't restart. The rcapache script just says "failed" and I get this in the apache error log: PHP Fatal error: Unable to start session mm module in Unknown on line 0 Not too helpful! Looks like I'm missing something PHP wants. Any ideas? -- "...our desktop is falling behind stability-wise and feature wise to KDE ...when I went to Mexico in December to the facility where we launched gnome, they had all switched to KDE3." - Miguel de Icaza, March 2003