Data conversion testing project

I am working is in Data conversion project. I know how to write SQLs, but i never got an opprtunity to work on a Data conversion testing project. I just wanted to see wheather anybody out there with this experience. Can you explain me the whole process and validating the source and target data in vb to .net application. How to write sqls with using business rules? Please help me.....

You can easily find all that by investing some time in web searching.