Maybe I am reading it wrong, but your question doesnt make sense. If you are submitting a link to digg, you do it through digg. And, what do you mean by digg sites? Perhaps you want to rephrase your question...
uhh, that didn't help much more... If you want to digg (vote for) a link/page you can either do it on digg.com or on the page itself if it has one of those digg link icons. If you want to submit a link/page to digg. You need to do it at digg.com. There's also a firefox plugin that helps you submit pages to digg, but that just speed the process of submitting through digg.com.
What is Social Bookmarking? http://www.speakingandmarketingtips.com/social-bookmarking.html 30 Largest Social Bookmarking Sites http://www.ebizmba.com/articles/social30.html Adding social bookmark links to your blog or web site http://www.toprankblog.com/tools/social-bookmarks/ Hope this help.