I recently upgraded my PhpED from the Standard version to the Professional version. When trying to set up my DB Client to connect to my (remote MySQL) database, the whole program locks up (have to end process). I tried it several times. If I give it the wrong port number I just get a "database not found" error. I'm running 5.01 Pro (5029) under Windows XP (SP2). Everything else behaves normally. Would this be caused by an installation error, a settings error, user error?

Definitely, it is not caused by PhpED. You may want to check if libmysql.dll that you installed into PhpED directory matches your server version. If you did not install libmysql.dll, you have to do it. What comes with PhpED is libmysql 3.23 and therefore has to be upgraded. Sorry, we can't do it for you due to strange licensing policy they established for the library.

Incidentally, I noticed with 5.0.1 that the installer still overwrites the library file. So if you haven't made a copy of it, you have to once again go the the MySQL site, download it, and install it - after bumping up against the fact that you're running an old library when you try to use it.

Can the installer just leave the installed version alone? Perhaps the library shouldn't even be installed (after all, I know of no 3.23.x installations anymore), and the IDE could just give a friendly error message with a helpful link to the appropriate area of MySQL's site when the user tried to do something. And once it's installed, treat it as a user config file, putting it with other config files and not replacing it on updates.

I think this would increase PhpED's user-friendliness in this area quite a bit, not to mention cut down the number of posts about it on here.

I wasn't aware I had to add the .dll to the PhpED directory. I guess I assumed that since it came with the package that it would already have the correct version. I agree there should at least be an alert box the first time you use it warning you about the outdated version. However my local MySQL library was unchanged by the installer.

probably, you're talking about your library that is not in phped directory and threfore it's not used by it.

On my local machine I use MySQL 5.0, on my remote server I use MySQL 4.1. I updated the libmysql file to a 4.1 version, and have no troubles connecting to my local database. However when I attempt to access the remote server, the whole program becomes non responsive.

Are you sure that you can access your remote server directly at all?
In most if not all cases it's not possible.
What you need to connect to remote database is ssh tunnel for port 3306.
Please consult on the matter with your ISP/Hosting/Network providers.

I have no problem accessing my remote database through the SSH client. However when attempting to use the DB Client, with an updated libmysql.dll file, the whole program locks up and becomes non responsive. This happens 100% of the time.

I have some doubts that the SSH client has any relation to databases. It may help to connect to them by providing tunnel and without this tunnel you can not connect to the database. It's what I meant under "directly".
In other words, I'd suggest you to continue running ssh tunnel and connect to the database through it. For example you may run
ssh -L localhost:3309:localhost:3306 myserveraccount@myservername
and in the account settings for this server you'll have
hostname: localhost
port: 3309
username: <yourdbsername>
password: <yourdbpassword>