[texhax] line spacing

[mr at xosoftware.dk]

I have a document with text in two different 
sizes: 10pt and 12pt. It seems that by 
default the line spacing between the two are 
the same. I would like to make the space 
between lines with text size 10pt to be 
smaller than that of text size 12pt. 
I have done some experimenting with 
\linespread{size} but this seems to only work 
for the whole document. 
Can anyone help me?
Thank you
Martin