I also run Movable Type for my weblogs (including Ask Dave Taylor!) and have spent way more hours than I want to think about figuring out how to customize and tweak it to do specific tasks and work in certain ways. I've even delved into the source code itself and "improved" a few things, but that's another story.

To do what you're asking, you need to log in to the MT administrative interface, which is known as mt.cgi. You'll need your account and password, though it's entirely possible that it will remember your credentials from the previous time you logged in and automatically take you to the main MT administrative screen.

At that point you should have a navigation menu on the left side that has three sections, POST, MANAGE and UTILITIES. The POST section lists New Entry, Edit Entries and Upload File. The MANAGE section lists Templates, Categories, Notifications and Weblog Config. The UTILITIES section, finally, has Search Entries, Import/Export, Rebuild Site and View Site.

The Import/Export feature is a great one for backing up your blog contents every so often (it creates one huge HTML file that has every entry and every comment for an entire weblog. Nice!) but let me stay on topic, not digress. I'll talk about Import/Export at some point down the road...

Click on Weblog Config and you'll have a new screen of choices, most of which you do not want to touch once you have your weblog running properly: on the first screen the options are all about directory locations and domain names. There's a submenu along the top, though, listing the following choices: Core Setup, Preferences, Archiving and IP Banning.

Click on Preferences. Now you'll see a bullet list of the four sections on this page of preferences (confused yet? MT is not the world's most consistent interface from an HCI perspective): General Settings, Archiving, Publicity / Remote Interfaces / TrackBack, and Comment Configuration.

Click on Publicity / Remote Interfaces / TrackBack. Now, finally, you're where you want to be!

The first configuration option under the Publicity head has "Notify the following sites when I update my blog:" and check boxes for blo.gs and weblogs.com. Below that is a text input box, and it should already have at least one additional site you're pinging: rpc.pingomatic.com. You want to add the new feedster ping tool URL immediately after the last entry in this box: scroll if needed, click after the last entry, press RETURN to get to a new line, then type in http://api.feedster.com/ping.

Good. Now scroll to the bottom of this preferences page and click on "Save". Once it's saved your update, you'll see a line that says "Your blog preferences have been saved. REBUILD to see those changes reflected on your public site."

Click on the word REBUILD and it'll pop up a little rebuild window. This cute little window has a pull-down menu with different types of rebuilds you can do, but the default is Rebuild All Files, and that's fine. Just click on the "Rebuild" button and get a cup of tea as it'll take a while.

Finally, the little window will indicate "all pages rebuilt. View site." and you should be done with the changes and ready to go. Congratulations!

I hope that helps you out!