How can I write a script to import just part of a file?

You can use the "ImportLink" command. You import a file manually and specify the range of rows in the dialog. Be sure to check the option to link the file. Then in your script, use "ImportLink" to import into that same data object (with its specifications for which rows to import), but with a new file.

Note that the ImportLink command only works with text files, and not with Excel files. If you would like this command to work with Excel files too, please submit your request at help.graphpad.com