The official Google webmaster central blog published a news on 29th June, 2010 which states that :
Have you ever wanted to submit your various content types (video, images, etc.) in one Sitemap? Now you can! If your site contains videos, images, mobile URLs, code or geo information, you can now create—and submit—a Sitemap with all the information.
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.