On my late 2005 Mac Mini G4 1.5Ghz I just replaced my original 80GB Seagate drive after Disk Utility failed multiple times to repair “Invalid node structure”.
After installing a new 160 GB Seagate ST9160281A (5 years warranty, $112 Canadian), and booting from my Tiger Install disk, I found that Disk Utility would also not see the new drive. I took everything apart again (I love that cracking sound when you open the case) and found that the corner of one of those pieces of yellow tape had fallen off the Airport cable and a corner of it was caught in the ATA slot on the motherboard where the riser fits.
So, I carefully removed the tape and swabbed the riser contacts with a Q-Tip moistened in alcohol mouthwash. After drying, I put it all back together again and this time it worked.
In reassembly, I also noticed that there was still a bit of wiggle room, a little gap where the drive connector plugs into the riser, so I applied a judicious bit of extra finger pressure to the back of the riser in order to make sure it was seated properly and the gap minimized.
Also about reassembly, after reinstalling the Mac Mini’s case, DVDs would not eject. The reason for this was that I had an alignment problem after incorrectly mounting the Airport device on the front right hand corner of the DVD drive.
I referred to http://www.smashsworld.com/2005/01/mac-mini-complete-technical.php and the excellent document http://str.smashsworld.com/?mac_mini.pdf. This clearly showed me that the Airport card is supposed to be mounted on the notched plastic clip at the BACK right-hand corner of the case.
I had not been able to mount DVDs at all before starting the work, so to start with I could not even boot up the install disk to run Disk Utility, but that was resolved easily enough after removing the case. After cleaning the Mac Mini inside with lots of canned air and then vacuuming, I carefully squirted a few extra shots of canned air through the mouth of the DVD drive, and then it was working again.