Took me quite awhile to figure this out, so hopefully the following info will save someone else a bunch of time. In short, the screen resolution/refresh rate that Ubuntu 8.04 has for the emachines E17T4W monitor does not work. I needed to bump up the refresh rate from the 60Hz that Ubuntu 8.04 is set at to 76Hz to get the monitor back to the sharpness it had running Ubuntu 7.10. In order to do that, I needed to modify the xorg.conf file. So here's how to do that:
gksudo gedit /etc/X11/xorg.conf
Identifier "Configured Monitor"
Vendorname "Generic LCD Display"
Modelname "LCD Panel 1280x720"
# 1280x720 @ 76.00 Hz (GTF) hsync: 57.15 kHz; pclk: 96.93 MHz
Modeline "1280x720_76.00" 96.93 1280 1352 1488 1696 720 721 724 752 -HSync +Vsync
Note: After restart, you'll need to select the 76hz from the drop down menu: