Need guidance on using CSVDE to import one field only

We have a Server 2003 AD environment with Exchange 2007. I need to add a set of numbers to the birthDat attribute in the AD Schema, but make no other changes to AD.

Would someone provide some guidance on how to do this effectively please. I've used CSVDE in thee past and some issues, and I;ve never attempted to update just one attribute on existing User objects. I dont want to negatively impact other attributes or objects themselves.

Thanks!