Everything to be done to install Arch Linux can be found in the Arch install guide at https://wiki.archlinux.org/index.php..._Install_Guide
and as well, it is a good idea to read the Arch beginner's guide at https://wiki.archlinux.org/index.php/Beginners'_Guide
. It is highly recommended if you have never installed it before, to print these out. They will save a lifetime of hassle. Arch is not something that you can do very well if you don't know what you're doing first. Follow these to the letter (I myself have memorized them now, I've done so many Arch installs), and you will never see a problem. They tell you what to install when, How to set up, everything.
To switch to another login manager, edit /etc/inittab, as so:
# 0 Halt
# 1(S) Single-user
# 2 Not used
# 3 Multi-user
# 4 Not used
# 5 X11
# 6 Reboot
## Only one of the following two lines can be uncommented!
# Boot to console
# Boot to X11
# -8 options fixes umlauts problem on login
c1:2345:respawn:/sbin/agetty -8 38400 tty1 linux
c2:2345:respawn:/sbin/agetty -8 38400 tty2 linux
c3:2345:respawn:/sbin/agetty -8 38400 tty3 linux
c4:2345:respawn:/sbin/agetty -8 38400 tty4 linux
c5:2345:respawn:/sbin/agetty -8 38400 tty5 linux
c6:2345:respawn:/sbin/agetty -8 38400 tty6 linux
# Hypervisor Virtual Console for Xen and KVM
#h0:2345:respawn:/sbin/agetty -8 38400 hvc0 linux
ca::ctrlaltdel:/sbin/shutdown -t3 -r now
# Example lines for starting a login manager
(This is the login manager I've chosen)--->x:5:respawn:/usr/bin/slim >/dev/null 2>&1
#x:5:respawn:/usr/bin/slim >& /dev/null
# End of file
... Simply uncomment the one you want to use. If it's not there, add it.
Oh, and Ubuntu cd = no. You're better off to fix with Arch's own live cd. Ubuntu and Arch are two completely different animals. One uses debian, the other tar.xz (source). If you are going to use a live cd to fix something, you need to use one that uses the same file system.