[Scribus] creating a book

[tibe]

I find ps utils so nice,
and the wiki "how to make a booklet" give me the right way to follow,
but now i have this problem, the command to rearrange the pages into a 
booklet is

psbook %filterinput | psnup -2 -p%psl | psselect -e %filteroutput

now i want to create a booklet 240mmx120mm, not in A5 format.
I think i must use "psresize", can someone help me using this?
I have no idea where in the command line i have to put psresize with his 
options...

Luca