Dallaglio, who played 85 times for England and was part of the world Cup-winning team of 2003, gives an assessment of each team's chances and offers an insight into the England dressing room before big matches.
He has also written the magazine's weekly Comment page, where he analyses the challenges facing new England coach Martin Johnson.
It is the first time the magazine has opted to use a guest editor for the magazine.
Sport's editor-in-chief Simon Caney, who is standing down for the week, said: "When we decided we'd like a guest editor to front our Six Nation coverage, there were very few names in the frame. But Dallaglio is an icon, who commands respect from everyone in the game. He knows his stuff inside out and he's a nice bloke, too."
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