There's been some speculation of late that multiple pages with the same description tag are treated differently.
http://www.seobook.com/archives/002030.shtml
http://tropicalseo.com/2007/the-resu...tags-are-back/
However, the meta description tag isn't that important in the grand scheme of things, so I wouldn't worry too much either way. The Googlebot will use a snippet, although it's difficult to control which section of text it will grab from a page.
I'm not familiar with MS Expression Web, so perhaps others could help you there.