You can submit your site to yahoo by going to site explorer here, https://siteexplorer.search.yahoo.com It's a simple process that succeed after a verification by META tag or uploading a file to your site. Good luck!
Yahoo can read sitemap.xml as well as Google did. You should not worry too much, even if someone might tell you that Yahoo only knows "urllist.txt". Yahoo was used to stick with their own urllist.txt format and had to change and accept sitemap.xml since the last one format is more popular then their own one.
Hey guys Yahoo! supports the Sitemaps format and protocol as documented on www.sitemaps.org. It can provide us a feed in the following supported formats. We recognize files with a .gz extension as compressed files and decompress them before parsing.
The standard XML powered sitemaps are nowadays compatible with all major search engines like Google, Yahoo as well as Bing. Once uploaded to your server, simply tell the engines about that and they would follow the links and URLs. You can create your webmaster tools on all the three portals easily and from your member panel, import the sitemaps.