my iMac G5 becomes corrupted and must be rebooted with install DVD

I'd guess your hd is getting corrupted.

Should run disk utility off of startup disc.

I'd guess replacing the hd is in order. Could run off of an external hd.

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I suspect disk corruptions.

verify & repair your startup drive

To verify & repair you file system on the startup drive, you will need to run disk utility from you installation DVD.

This article will tell you how to get to disk utility. Once in a disk utility, you can go and attempt to recover the disk.

http://support.apple.com/kb/TS1417

To repair your startup drive, you will need to run disk utility from your startup DVD.
Mac OS X 10.4: About the utilities available on the Mac OS X 10.4 Install DVD

http://support.apple.com/kb/HT2055

How to run disk utility from your startup DVD.

1. Insert your startup DVD into your reader. Power down your machine. Hold down to the c key. Power on your machine. This will bootup your startup DVD.
2. This will bring you to a panel asking you for your language. Pick your language.






3. You you come to the Install Mac OS panel. Do not install.
4. Click on Utilities menu item. This will give you a pulldown list of utilities.
5. Click on the disk utility.
   
6. You are now in disk utility. Pick your disk. Click on repair it should be on the lower right of the panel.
7. Once the repair completes successfully, you should update your permissions.

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You need an external Firewire drive to boot a PowerPC Mac computer.

I recommend you do a google search on any external harddrive you are looking at.

I bought a low cost external drive enclosure. When I started having trouble with it, I did a google search and found a lot of complaints about the drive enclosure. I ended up buying a new drive enclosure. On my second go around, I decided to buy a drive enclosure with a good history of working with Macs. The chip set seems to be the key ingredient. The Oxford line of chips seems to be good. I got the Oxford 911.

Has everything interface:

FireWire 800/400 + USB2, + eSATA 'Quad Interface'

&

save a little money interface:

FireWire 400 + USB 2.0

This web page lists both external harddrive types. You may need to scroll to the right to see both.

http://eshop.macsales.com/shop/firewire/1394/USB/EliteAL/eSATA_FW800_FW400_USB

I recommend a new hd because you have been having the problem for awhile.

You never can be sure. I'd go with an external hd, because you can always use it as backup if it doesn't solve the problem.

There are better file system repair utilities, but I think not in your case.

Disk Warrior

http://www.alsoft.com/DiskWarrior/

Robert