i own a computer with LInux & Xp . my friend owns a computer with XP. my friend wants to connect with me by dialing to my computer. i dont want to use internet to connect with my friend . that is i want to act as an ISP . what i have to do. my friend dials to my computer and only telephone rings going on . how to make my computer respond to the dials and provide a user with a login screen?

is your friend trying to connect to CP or Linux? or does it not matter as long as he can connect?

mgetty can answer your modem ....
it may not be installed so you might have to install it
you will have to edit
/etc/mgetty/dialin.config
possibly
/etc/mgetty/login.conf and mgetty.conf
it should install with some sample configs

and set mgetty to listen to the modem
modify /etc/inittab to include
(adjust S3 and ttyS3 to your moden device) S3 is like Winblows COM4
23 is to listen for run level 2 and 3
-s 57600 is 56K
-x0 is low debugging level

S3:23:respawn:/sbin/mgetty -x0 -s 57600 ttyS3

if someone wants to dialin using winblows you may have to modify
/etc/ppp/options (add a DNS entry)
/etc/ppp/pap-secrets (to allow the use of /etc/passwd for login)

sounds like a fun project