Extremey Slow (or dead) Sites

I've got two sites hosted at dreamhost, each one with a Wordpress Install and a MediaWiki Install. Both have been getting slower and slower over the past month, to the point where now both take over 30 seconds to load, if they load at all (I usually get some sort of error message). Here are the URLs:

www.mrlocke.net
www.faithbridgechurch.org

I've gone back and forth with Dreamhost supports, and they've tried everything from moving me to a new server, to having me split the two sites into two separate users. They've also said that it might be something with the scripts I'm running, but they can't isolate which one. I know others who run multiple sites with both Wordpress and Mediawiki, and don't have the same problems, so is there something else I'm doing wrong? Please help if you can...

Both sites result in:

"Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, webmaster@mrlocke.net and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request."

This is a problem with whatever is being used to serve your pages, be that PHP or whatever it is you programed them in.