128mb wasn't enough I guess. :p
Here are the changes I did (on UBCDv5b12):
~/UBCD is the content of the iso.
~/ophcrack is either the Vista or the XP-version of Ophcrack, extracted form iso.
Move ~/ophcrack (the folder) into ~/UBCD (so the ophcrack-boot-folder is at ~/UBCD/ophcrack/boot)
Change every occurence of /boot with /ophcrack/boot in ~/UBCD/ophcrack/ophcrack.cfg
Now you only need to add a "shortcut":
Add the following in the bottom of f.ex. ~/UBCD/ubcd/custom/custom.cfg
MENU LABEL Ophcrack
Start OPHCrack with tables for Vista (or/and XP)
The last step, is to build the iso.
For this you need the executable mkisofs.
I couldn't compile it myself but I did find a pre-compiled in the app Visualhub (a video-converter for Mac – no longer supported).
Open Terminal (or CommandPrompt, on Windows) and navigate to ~/UBCD/ubcd/tools/
Now you have to execute the ubcd2iso.