Recognize first emtpy Cell in column

How can i code to copy range (which is not always going to be the same) from one book.sheet to another. The code would have to look for the first emtpy cell in
the latter book, and thenn paste.
Currently i select all cells (which i dont want, i need to select all data cells without header row) and paste in new book after selecting range. Range is dynamic , so i have to code to look for first emtpy cell where i need to paste.

any ideas.
Thanx

sub
ActiveSheet.Cells.Select
ActiveSheet.Cells.EntireColumn.AutoFit
ActiveSheet.Range("c1").Sort _
Key1:=ActiveSheet.Columns("c"), _
Header:=xlYes
ActiveSheet.Cells.Select
Selection.Copy

Workbooks.Open "C:\Documents and Settings\User\Desktop\ALLTIE.xls", , False
AppActivate "Microsoft Excel"ActiveSheet.Cells.Select
ActiveSheet.Paste
end sub