Here's the URL:
http://www.microsoft.com/reader/prom.../free_shop.asp
Latest version. If you're installing it on a 16Mb Axim go ahead and choose system memory for the install even if it comes up short. After the install you will get a prompt on the Axim to replace the previous version. This will get the memory used back down.
Also check out the 'Downloads' section for a nice selection of free dictionaries. English, German, Spanish....:D