That's a long time since i've installed ppp but here is what i can tell you :
Clearly the package (ppp-mppe-2.4.1-7) you're trying to install conflicts with an already installed package (ppp-2.4.10). The plain ppp 2.4.10 was surely installed during RH installation. If you compare the contents of both packages they quite identical except for the '-mppe' that's added in the path. As i can gather ppp-mppe comes with firehat and plain ppp with RH. I can't say if you really need ppp-mppe to complete your installation (a quick look at
http://rpmfind.net shows that pptpd packages don't require a ppp package). As you already got a more recent version of ppp (the 2.4.10) , you could try skipping the ppp-mppe installation. Otherwise you'll need to remove the 2.4.10 beforehand..
Hope it'll help.