YTD is the performance of the fund year to date...example, if the fund was worth $1.00 at 1/1/2008 and at 6/24/2008 its worth $1.05, youre looking at a 5% gain in the fund YTD.

Yield is the percentage you earn in interest each year...currently 4.78%...you earn this on top of what the fund gains, its guaranteed and not computed in the YTD calculation.

Hope this helps!