If you are using WordPress you should also be using the excellent Google Sitemap Generator plugin. Nothing helps a search engine index your page faster than having a sitemap.
Don’t let the name fool you as the sitemap generated is not just for Google, both Yahoo and MSN also follow the same standard. Yeah I know what you’re thinking, “MicroSoft following a standard???” well in this case they do!
After you install and activate the plugin a menu item will show up under your options tab. From there you can set a few options (defaults should be fine) and build your sitemap. The plugin will even ping Google to let them know you have updated your sitemap!
There is one area which might give you trouble. You need to either change the permissions on your root directory (not always a good idea) or you can create a few empty files with the proper names and set them to 666 on their permissions.