However, thanks to the great people at the Ubuntu forums, it seems like I have found a fix that works. Special thanks to clhsharky for this tip. You can read the full post here.
But here's the gist of it (I've tried this on an ATI x1400 Video card, and it stops the external monitor from flickering):
Update (August 20, 2010): Seems like the rc7 release is available. You might want to download that instead... (see the comments section for more information)
Update (August 21, 2010): As Ryan suggests in his comment below, the rc6/rc7 candidates may contain a security flaw, so you may want to read that first before proceeding...
Go to http://kernel.ubuntu.com/~kernel-ppa/mainline/v2.6.34-rc6-lucid/
and download the following files and install them in this order (depending on which processor you have)
For Intel (x86/64) based processors download and install (installing as in double click the .deb files after downloading it and click install..) the following in this order:
For AMD processors download and install the following .deb packages in this order:
Finally, after you restart, you'll be able to choose the rc6 kernel while you boot, which should fix the problems.
Again, this may not work for all ATI cards, but it seems to work for mine!
And boy is Ubuntu fast... it loads in ~ 35 seconds on a 4 year old laptop. Impressive... and now I also use dual monitors if I want to!
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