RADIUS question as well as PPTP

[BlackEvo]

If implementing VPN, wouldn't VPN eliminate the need for a RAS? would it be effective to implement RADIUS with VPN or is RAS incoporated with RADIUS?

Ive read that PPTP isn't really going to be common, but, are the ideas behind CHAP and PPTP the same?

I read things right, chap is done to encrypt passwords and login before its sent to a server, but this is for RAS, correct?

where PPTP does prety much the same thing, ensuring a user is who they say they are with a login and password?

thanks for any help