Can't open Java preferences

Do you have one or more external backups of your disk and your data, and do you have your installation DVD disk?

Java for Mac OS X 10.6 Update 5

The Java update might cure this. Do try it.

I would encourage getting a second external disk and creating a full-disk backup using Disk Utility or analogous in general. For what I'm going to suggest here, I'd prefer to have at least two external backups, to avoid data loss, and Time Machine restorations can sometimes be wonky.

The suggestions? Three-fold. The first potential solution here is going to involve the download and reinstallation of a Mac OS X combo patch kit (the combo kit, and not the delta kit), then load the Java update and other kits. (Have a backup.)

Second, booting and installing a fresh copy of Mac OS X over the top of your existing disk, and that involves the need for a Mac OS X client installation DVD disk. Then updating the new installation on the internal disk to current. (And I'd prefer to have backups here, to avoid data loss.)

The third and most involved suggestion is the nuke-and-pave reinstallation over the top of what you have here. The use of one of your external backup disk image copies as a migration source, and booting and using the distribution DVD to wipe the existing internal disk, and then perform the import from the external copy.

And do get yourself a copy of the Snow Leopard DVD.

Computers fail, and installation disks and backups are your path back to operation.

I've tried that and I can't run it.

Why not? What happened?

Is there some reason why you don't want to update to 10.6.8?

The easiest way is simply to choose "Software Update" from the Apple menu. You may have to do it more than once in order to get all the available updates.

Yes; it can seem odd. Downloading a copy of the combo update and re-applying it is a longstanding technique for dealing with corrupted updates. Updates can go wonky during the installation for various reasons, and various hard disks run three to six uncorrected hard errors per terabyte, give or take. Reloading an update can clear some of these cases.