If you use an HDMI to VGA adaptor and get a black screen you may tweak the config.txt to solve the problem.
If you open config.txt you will see that there are plenty of lines commented out that change the behavior of the HDMI output in the Raspberry Pi. This is the configuration that made my Raspberry Pi work OK using an HDMI to VGA adapter:
disable_overscan=1 hdmi_group=2 hdmi_mode=35 hdmi_drive=2
Source: http://www.raspberrypi.org/phpBB3/viewtopic.php?f=76&t=33477