Do you need 2gb?
Most people go 2gb for BF2 or cad
Im assuming your current memory is prob 2-3-2-6 1t
the mushkin will be 3-3-3-8 plus running 3 sticks will mean 2t rates.
Putting in the extra stick will slow all your ram down to 3-3-3-8 and push you to 2t rates. Also only your current ram will be in dual channel.
It will slow your ram down a fair bit putting in the new ram but prob not enough for the average person to notice.
If you feel you need 2gb then go for it, if you can live without it then I would even if it seems like a bargin.