Q: How do I connect my iMac G5 to an HD TV as display monitor?

If you have a G5 Mac, that means it is a PPC based iMac and not an Intel based iMac. That means your post is in the wrong forum. It should have been posted to the https://discussions.apple.com/community/desktop_computers/imac_powerpc

If you are not positive you have a G5 iMac then click the Apple symbol in the upper left of your display, then click About this Mac.

Good luck.

Hi,

Apple has never been very friendly with display ports, changing them nearly each generation.  The iMac G5's had the MiniVGA port. 

Assuming your HD TV has a VGA port (many do) you just need to pick up a MiniVGA to VGA adaptor.  Something like this:

http://www.ebay.co.uk/itm/Apple-Mini-VGA-to-VGA-Display-Adapter-eMac-iMac-PowerB ook-M8639G-A-NEW-/351420170130?hash=item51d2463f92

You'll need to connect separate audio cables if required too.

The iMac G5 only officially supported Video Mirroring meaning you'll only get what you can see on the Mac - rather than a second display but there is a fix called Screen Spanning Doctor that you might like to try at your own risk: http://www.rutemoeller.com/mp/ibook/supportlist_e.html

Regards,

mrtotes