I have minecraft.jar I downloaded from minecraft.net placed at /home/daboross/minecraft/minecraft.jar
When I use the command that minecraft.net says to use in terminal, I get this:

daboross@ubuntu:/home/daboross$ java -Xmx1024M -Xms512M -cp /home/daboross/minecraft/minecraft.jar net.minecraft.LauncherFrame
asdf
Exception in thread "main" java.awt.HeadlessException
at java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:173)
at java.awt.Window.<init>(Window.java:477)
at java.awt.Frame.<init>(Frame.java:419)
at net.minecraft.LauncherFrame.<init>(LauncherFrame.java:20)
at net.minecraft.LauncherFrame.main(LauncherFrame.java:167)