I tried to upgrade my version of KDE while running in Gnome. I essentially ended up reinstalling my old version of KDE. Now when I start up my computer (dual boot) after selecting "linux" I get to the localhost login screen. The only thing on my screen are the fields for username and password, with no way to select what desktop environment to boot in. I would like to be able to boot into Gnome or KDE but I'm not sure how to make this possible.

try this command :

switchdisk gnome
or
switchdisk kde

to switch between the two env.

to boot to the gnome run this command:

gnome-session

to boot to the kde run this command:

startkde

startx command to run the defualt env.

you can create this file on the /root

.xinitrc
and add this line on it to auto start with gnome:
/usr/X11R6/bin/gnome-session

Probably your OS couldn't find KDM or GDM. Both are the graphical login managers with a lot of resources. If the system couldn't find the specific screen, then the system will use the XDM which is a very simple Graphical login manager. What you need to find out is: How to change the graphical login manager.

Case you don't want your machine to always boot on graphic mode, you can change your /etc/inittab so you will always have the beautiful and perfect console mode!! And case you do that, then you can follow the instructions the other guy posted.