1. Extract the directory "art/intrface" [sic!] from the FO1 master.dat archive to your HDD
2. Copy the FRM interface files you want to replace from the extracted "art/intrface" directory into your Fallout 2 "data/art/intrface" directory. If you don't know what are the important interface files: use a FRM viewer (can be found in the NMA download section) to look it up.
3. Have fun with the FO1 interface.