ok, I'm not the RedHat guru here, but if you need php, then you just search php on rpmfind.net.
here you can find php for RH8:
again: be sure you have all the depencies installed.
If you wish to install that rpm you have know on the other hand, just install every depency it's asking for.
I don't think it's hard to see that zziplib != libz.
I have no idea what's the difference between the two php rpm's though.