Screen resolution - 600x480 -> 1024x768

[Robert Citek]

How does one change the screen resolution under xfce4 4.2.2?

I've installed Ubuntu using the server installation method and then  
installed xfce4 using apt-get on some low-end hardware (<400 MHz,  
<128 MB RAM, <10 GB HDD).  During the installation of the X Window  
System, Ubuntu asked me what screen modes I would like to which I  
answered 1024x768, 800x600, and 640x480.  When xfce starts up and I  
go to "Xfce Menu > Settings > Display Settings" only 640x480 shows.

I know the video and monitor can do 1024x768, because I can boot  
Knoppix 4.0.2 on the machine just fine with icewm.

Where would I look to enable 1024x768?  Is this an xfce issue, an X  
server issue, a driver issue, something else?

Thanks in advance for pointers in the right direction.

Regards,
- Robert
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