Thank you for your reply, WoodyZ!
What do you mean by V2V? I really don't know much about emulating.
So if I understood you right, it is possible to limit the virtual disk space before I install WinXP and Win7? If so, I could just delete the OSes and reinstall them. I haven't got any data on the virtual machines \ virtual hard disks I still need. I cannot remember any chance VMware would have given me to choose a smaller virtual disk, though, because the first time I was able to choose the amount of disk space I wasn't able to make a smaller disk either.
But even if I needed the data, it is possible to move data (e.g. photos or movies) from WinXP \ Win7 to Mac OS, right?
The .tgz-file is added. Maybe this helps at some point.
EDIT:
I found an option to "remove" the virtual hard disk (right-click on the OS listed in VMware -> settings -> hard discs -> advanced options -> remove hard disc). Might this be useful? To remove it and create a new one which is smaller?