file >
create

FileSystemObject.CreateTextFile(filename[,overwrite[,unicode]])
to create a new file (eg .txt .asp .php .jpg .pl ...any file)

FileSystemObject.CreateTextFile(filename[,overwrite[,unicode]])

true: allow overwrite
false: disallow overwrite

Create a file source code 1:
<% ' source code : allow overwrite
dim fso,newfile

set fso=Server.CreateObject("Scripting.FileSystemObject")
set newfile=fso.CreateTextFile("c:\mypath\newfile1.txt",true)
newfile.WriteLine "text here"
newfile.close
set newfile=nothing 
set fso=nothing     
%>

Check a file source code -------------
<%
if fso.fileExists ("c:\mypath\newfile1.txt") then

end if

set fso=nothing       
%>

you may use 

<%
Set AppendText    = "(appent a text line after old file)"
Set fso          = CreateObject("Scripting.FileSystemObject")
filename       = server.mappath("c:\mypath\newfile1.txt")
Set appendfile = fso.OpenTextFile(filename,8,True)
appendfile.writeline(AppendText)
appendfile.close
Set appendfile = Nothing
Set fso         = Nothing
%>