.GCT is essentially nothing more then a tab delimited text file.
I mentioned in an article how to create a delimited text file using chars like CSA (comma separated value, essentially Comma delimited value)
Read Tab Delimited
So the question is, are you asking how to convert a text file to tab delimited and save it as a .gct?
and if you are using a listbox or are you trying to convert a actual file.
If you are using a listbox and want to save it tab delimited, I can help.
If you are converting a file you will have to use string manipulation and streamreader / writer to add a tab space after every word , that will take me some time to make it work, so , let me know which direction you are going.