Okay, I've now migrated all my old posts from my old blog to here. I did this with the help of this tool, which I modified to use a MySQL database (my blog's database) as a source, instead of my blog's XML-RPC interface. So that copied across all old posts. Currently, comments aren't copied over; I plan to write a similar little tool to do this at some point.
People arriving at pages on my old site are redirected to here. This is done through the use of a .htaccess redirect on the old site to a Python CGI script. The script figures out what the new name of the page it was asked for should be, and redirects the user. The problem with this is that Blogger is occasionally clever about post names, leaving out the word 'an', say, if the name is long. So some pages redirect to nothingness. I will take a look at the 404 errors I'm getting and see if I can put together a solution.
But I'm very, very glad to be rid of Wordpress.