Would you ming providing a screenshot about them grayed out ones? Also, what version of iTunes and OS X? Try searching for them in finder - if you find any, drag it back to iTunes. It just might be that iTunes has lost track of them fies whereabouts.
Download the latest CHUD-package from apple, 3.0b24 or what the version was.. it has a friendly app called BigTop, a frontend for top, vm_stat and network among some other things... Works well in Jaguar and WWDC Preview
I've noted that sometimes when you grind down some rail that ends in ground level, you get stuck below the ground. Also, on my G4/350 sawtoot, THPS3 runs much quicker than THPS2, this is due to better code optimization etc.
Well, I've never used any symantec product in OS X... I do defrag my disks via OS 9, using a speed disk profile made for OS X alongside other applications...