var rows = tableid.rows;
var len = rows.length;
for(var i=0 ;i<len; i++)
   rows[i].cells[2].style.backgroundColor = "yourcolor";关于日期的常见操作
http://community.csdn.net//Expert/TopicView2.asp?id=4360247&datebasetype=now
js FAQ贴
http://community.csdn.net//Expert/TopicView2.asp?id=4356360&datebasetype=now
DHTML手册,js手册,dom手册下载
http://community.csdn.net//Expert/TopicView2.asp?id=4356325&datebasetype=now