I also had similar problem regarding writing a .dbf file from .xls and .txt file. I had a .xls file which i want to convert to .dbf file for analysis. I converted that fie to .txt file using MS excel. Then using ArcGIS - Arc Catalog, i created a Personal Geodatabase (gdb) in same folder. Then i imported the .txt file to that gdb. Then i exported the gdb file to dbf file in Arc Catalog environment. I hope u might have found a solution. Its a late reply. But i like to share this info.