For the common Internet knowledge (we just spent 2 hours hunting for this information):
You must add debian-installer/framebuffer=false kernel boot option to install Ubuntu Hardy on compaq 6910p. Otherwise you get black screen on boot.
For more info:
I hope this is fixed in Interpid. At least after installing and upgrading packages no tricks are needed.
Update 31.3.2010: This issue STILL exists in Ubuntu Karmic. Looks like i'll have to make a bug report when Launchpad is online again.