In our system we have part numbers that contain a point (dot), e.g. "108710.03". I need to pass this number, but without the part following the dot, to an archive system, i.e. "108710" only. How can I achieve this with GuiXT?

The simplest way is to use the "pattern" option of the Set command:

Set V[partnumber] "&F[RMMG1-MATNR]" pattern="%."

(supported as of GuiXT 2007 Q1 1)