After 2 weeks of using 10.5.7, my comp started getting slower, windows took forever to open/update, then itunes wouldn't read/import CD's, then started hanging, then wouldn't boot.
Out with the Boot DVD, Disk Utility chokes on "Invalid Node Structure" and can't repair the drive. And I don't have a backup (hits head against wall many times). And I don't know what Invalid Node Structure means.
Scrambling to find a solution I researched and found the unix utility "fsck_hfs -fy" (built into the operating system!!) and ran it from Terminal from boot disk. Took 3 passes and repaired the directory enough to be readable.
MADE BACKUP (Whew!). Did Archive and Install. Backed up again. Zeroed internal drive, restored from backup. Updated from combo package to 10.5.6. Backed up everything again.
So far, everything is working fine (had to reenter Logic Studio registration & serial #)
LESSONS LEARNED:
1: Backup, backup, backup, and do it some more
2: Never install OS X from software update, only use combo package
3. Wait a while before upgrading ANYthing.
3: Macs are not invincible.
4. I was an idiot for not doing regular backups, but I'm smarter now, and humbled.
If you should ever run into this "Invalid node structure" problem, check out TheXLab. Without their useful info, my work would have been lost forever from an Apple Store Wipe and Reinstall (or costly drive swap)
Hope this may help anyone else that may run into this problem.