DECLARE @ArticlesTable TABLE(ArticleId INT)

Fill it up:

INSERT INTO @ArticlesTable

 SELECT dbo.cmsArticle.ArticleId

FROM   dbo.cmsArticle

WHERE dbo.cmsArticle.CreatedDate<'01/01/2008'

Use it:

DELETE FROM dbo.cmsArticle WHERE ArticleId IN (SELECT * FROM @ArticlesTable)