Pinging with either Movable Type or with WordPress is pretty easy to do but the tough part is knowing where to ping. Here are the sites that I ping:
http://api.my.yahoo.com/rss/ping?u=http://(your weblog address)
For the most part these seem to work although I occasional get some errors back. Remember to register your weblog at http://my.yahoo.com before you put your address in there and while you are at it go and register at lots of weblog sites as well. Robin Good has created a great list of sites to register your blog with.