How to Get external datas in an existing file

[barewillysprl euphonynet be]

Hi,
using Menubar/Datas/Det external data and selecting a myfile.txt results
in Gnumeric opening a new window having the content of myfile.txt copied
and starting at cell A1.

How can one import those external datas:
1. in/from an existing gnumeric file?
2. and pointing to a given cell, for example H15?

Thanks for ant answer
Charlie