Since the Ubuntu forum is down I'll ask it here. If I install Ubuntu Server, and after that xfce4 (through the command line). Is it possible to run it than? By typing a certain command, or will it start by itself? Thanks.

first of all i never tried ubuntu,

1) considiring that its debian based i GUESS that when you install xfce through apt-get that it will install all the other needed packages for you such as Xorg and stuff, so you could give that a try.
2) if it will start automatically when booting depends on the setup of the default run-level. (for example this is what i have in /etc/inittab with Suse and the numbers are for example different on slackware, but the basic principle is the same, you will probably find explanation in your /etc/inittab on ubuntu)

# The default runlevel is defined here
id:5:initdefault:

# First script to be executed, if not booting in emergency (-b) mode
si::bootwait:/etc/init.d/boot

# /etc/init.d/rc takes care of runlevel handling
#
# runlevel 0 is System halt (Do not use this for initdefault!)
# runlevel 1 is Single user mode
# runlevel 2 is Local multiuser without remote network (e.g. NFS)
# runlevel 3 is Full multiuser with network
# runlevel 4 is Not used
# runlevel 5 is Full multiuser with network and xdm
# runlevel 6 is System reboot (Do not use this for initdefault!)

this means that runlevel 5 for me is when i use a desktop and runlevel 3 boots into a shell without desktop.

you can change the default runlevel for start up so that your server will boot into xfce when you start the computer. OR you prefer to boot into the shell by default, in that case you can simply type "startx" after you login to go to xfce.

3)here is a question i have!!! why do you want a desktop on your server at all?

I want one because it isn't a server, I just don't want to install all the useless software.

depending on the standard ubuntu install procedure that could make sense,

please let us know if this approach works or not and how you pulled it off, i'm sure plenty of peolpe are interested

OK. But I first have to wait to test it. I'm afraid lose my data, and my files are pretty important for school. But in a week, I'll try to have it done.
And does anyone know the command line code to install the log in manager if it doesn't do so by itself?
I'll also go and ask this on the Ubuntu forum, maybe someone has done this before me (looks logical to me.)

i'm sure it will work,
the only question will be if its more work to add packages to a server install to get the desktop you want
or if its more work to remove unneeded packages from a standard desktop install.

It will work... lol you will then be running xubuntu, which a lot of people do. Do a server install, then:

apt-get install xubuntu-desktop

-olly

i did it on my desktop. installed the server version. then i enabled the apt-sources and install xfce4. i then added gdm so that i would a login screen. and with gdm it logs in automatically without me typing my username and startx and such. I run gnome of my laptop but xfce on my desktop. so it should work without problems

A wiki page on server + light desktop installations:
https://wiki.ubuntu.com/Installation/LowMemorySystems