RPi Easy SD Card Setup - eLinux.org

Can only get 800x480 resolution in LXDE (Arch linux)
Known issue with distro package as of 17th April 2012 - there's some missing boot
config information. Creating a suitable cmdline.txt fixes it - type the following at the
Raspberry Pi command line:
sudo echo "dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 root=/dev/mmcblk0p2 rootfstype
Big black borders around small image on HD monitors
Out of the box, R-Pi graphics don't necessarily fill the whole screen. This is due to
something called "Underscan", and it can be fixed easily.
Note: the best solution is to disable overscan in display menu options (it may be called
"just scan", "screen fit", "HD size", "full pixel", "unscaled", "dot by dot", "native" or
"1:1"), then use the disable_overscan=1 option.
Edit the configuration file, see the instructions at R-Pi_ConfigurationFile.
Add the following lines to the configuration file...
If your display has no overscan:
disable_overscan=1
or if your display has some overscan:
overscan_left=-20
overscan_right=-20
overscan_top=-20
overscan_bottom=-20
Making the R-Pi graphics fill the screen is a matter of experimenting with the numbers
you put in the config.txt file. Change the numbers – try jumps of 5 or 10 at a time. Bigger
negative numbers reduce the black borders (so -40 means less black border than -20). The
numbers do not all have to be the same; you can use this feature to centre the display on
the screen.