The comment "it's been running progressively slower" implies that the drive may be bad. I use a product called Scannerz. You can get info on it under the Scannerz section at:
http://www.scsc-online.com
With that said, unfortunately, kernel panics can be caused by drive problems, software problems, or hardware problems, which pretty much means they can be caused by almost anything. In the booting process, the kernel reads files from the disk, and if the files are damaged (drive) or missing/corrupted/wrong permissions, etc. (software problems) it won't boot at all. Hardware problems mean that during the boot process the kernel fails to establish communications with the failed device.
Here are some links from Apple about kernel panics that might be of use to you:
http://support.apple.com/kb/TS3742
http://developer.apple.com/library/mac/#technotes/tn2063/_index.html
The first one is general, the second is more or less advanced.
I would try some of the procedures like safe-booting as described in the first because anyone can do it. If I'm not mistaken, at least on some of the newer OSes the first thing that launchd does is launch the kextd daeamon, which loads all the kernel extensions. If the files are corrupt due to damage on the drive it could happen, or if somehow or other one or more of the kext's being loaded are corrupt I think it could be caused as well. The latter **might** be revealed during a safe boot because it won't necessarily load all the kext files, but if one of them has problems you'll never know.
The posts from "justperry" came in while I was writing this, and he's right. If you have a bootable media and it will boot off of it, then you can be pretty sure the hardware is OK. If it can't do that then it's likely hardware. Disk Utility can be used to repair permissions and correct indexing problems. It can't, however, detect bad sectors or missing files.
If it can boot off of install media and Disk Utility does it's stuff OK and the problems persist, it would imply to me the drive is bad. The only way I can think of to test it would be to put it into target disk mode (FireWire) and then use another Mac with Scannerz (or another scanning utility) installed on it to do a surface scan on it. With Scannerz you would likely be looking for errors and/or irregularities (weak or marginal sectors) in the starting regions of the drive (0-5GB to be safe). In your case you likely wouldn't need to bother using a "normal" scan with Scannerz, but rather go right into "cursory" mode to configure your test (you already know you have problems, and it's safe to say they're in the boot region of the drive). If the problem can be traced to a kext file from an add-on app, then a full scan of the drive would be needed but I wouldn't use normal mode, I'd just do a surface scan-only over the entire drive in cursory mode.
Like I said at the start of this post, the comment "It's been running progressively slower" is symptomatic of a drive developing problems.
Hope this helps. Now you have several responses.
