I searched in the netbsd-help archive for a step by step instructions on how
configure ppp, but I've found only questions from many people on this
argument.

I've also searched all over the internet for a good FAQ, but the only ones are
for Irix, Solaris and SCO. I read them, they are very good FAQ, but
inapplicable to NetBSD.

Now, all I understand is that NetBSD have ppp built into the kernel, while
FreeBSD have ppp also out of the kernel.

The very good "Unix System Administation Handbook" fall down with ppp.

Well, I also, and obviously, read the man about pppd, and now all I know is
that there are too much options. ;-)
Pppd tells about some mysterious scripts into /etc/ppp/ but don't tell at all
how to create them, neither who really need them: pppd? The user, to start and
stop ppp? :-|

Could anyone please explain me how configure, start and stop a client ppp with
pap for dial-up connection with dynamic IP?

There is another thing I don't understand: pppd when started, seems to set
automatically the IP address assigned from the server (if dynamic), that's ok,
but I've got an ethernet board with an assigned IP address, how can I tell
pppd to do an "ifconfig ip-address alias"?

Endless thanks for any help. ;-)