iMac G5 PowerPC MacOSX 10.4.11 rebuild advice

I have a 5 year old iMac that has started to behave strangely.

First Microsoft Office, which had been running just fine for years, now won't open (an error required it to close). When I installed OpenOffice.org, that also showed the same message when I fired it up. Other apps are closing suddenly at a rate much higher than previously.

I have already applied advice I gleaned from the web, and forums. Problem persists.

I figure that I might as well do my very first rebuild, rather than spending ages trying to figure out the problem. With the PC, it was an annual event, so I got used to it, but I've never had the need to rebuild a Mac.

Are there any reliable web pages that tell how to wipe the hard drive and start again?

Thanks - that was helpful.

I had to reorder the discs - still on their way, but will get into it asap.

Current state of play

Have 3 Macs altogether.

iMac - G5 iSight - Tiger
iMac - Intel 2007 - Tiger
MacBook Pro 2008 - Leopard

The two iMacs have well-functioning disc drives - but I cannot find install discs for them, and the MacBook has a defective disc drive and won't accept discs (and that's the one I have original install discs for LOL) Have been sent replacement disc for the G5 iMac, but it won't boot from the replacement install disc, hence this thread. Have tried holding down C button, holding option then choosing drive, selecting icon in Finder clicking then restarting. Just sits at grey Apple screen and won't progress.

Went to Apple Genius (who also found that the Mac won't boot from the disc) - showed me how to create partitions on external drive and copy install files to there using Disk Utility restore. Also mentioned using 'target mode'.

At home, I created partitions as shown ... but ... it turns out that the drive I have (WD Pro II) will work for Intel Macs, but cannot be used for booting a PowerPC .
Still, by linking different Macs together and setting one as target, I was able to repair the hard drives of all them but this has not fixed the original issue of MS Office not working on the G5 (which sparked this whole enterprise).

I then spent yet more time on the phone with Apple, and they have finally agreed to send out more discs at no cost. These will be in the original format, namely two discs as would have arrived originally, rather than a single disc with everything on it.

At least I have now learned how to

• start up a Mac in different ways using the keyboard
• set a Mac into target mode
• link Macs together using firewire
• create and use partitions with install files on them
• repair hard drives for machines with no disc drive, or those without install discs (if another Mac has compatible OS)

Am now feeling quite confident that I can reinstall once I get it to boot from the discs - feels like child's play now that I've been through all this other drama.