Is it possible to restore an image to a machine and specify how big of a
primary partition I want the image to create?

What I want to do is to restore an image to a machine which has an 80GB hard
drive, but create a 40 GB partition and leave the other 40 unallocated to be
used for something else?

The default just seems to create one giant partition which uses the whole
drive.

Would something like this work?

Img pc1 NTFS 40000.

Am I on the right track at all?

Thanks