Hoople - 3:52 am on Jul 12, 2010 (gmt 0)
Bing still supports the older Sitemap XML. For Yahoo! the filename of the URL list file must be urllist.txt. A cr-lf delimited URL list. Both support sitemap ping of their respective supported file formats.
No indication on either of their help pages as to new format inclusion. I feel your pain, I also have lots of image meta data to include too that's missed by Yahoo! and Bing.