SED Help Needed

I am trying to retrieve part of a line from /boot/grub/menu.lst

The line is :

gfxmenu (hd0,0)/usr/share/gfxboot/themes/pclinuxblue/boot/message

I have figured out how to get this line into a file by itself.

sed '/gfxmenu/ !d' /boot/grub/menu.lst > /tmp/menu.lst.pcl_tc

What I need to do now or all in one step is end up with just the part that says "pclinuxblue" in the file.
So in essence I need to remove everything except what comes between "themes/" and "/boot".
These 2 parts are always there it is the "pclinuxblue" part that changes and I want to change.

Also I will end up writing this back with a new value lets say "$new" so any help on extracting and replacing this value is what I need.

Try the bolded part:

sed '/gfxmenu/ !d' /boot/grub/menu.lst | sed 's!\(.*\)themes/\(.*\)/boot\(.*\)!\2!'

Wow!! 8 minutes. I have spent the past 6 hours getting to this point. Guess I should have posted here long ago. Thanks again it worked perfect!!!!!!!!!!!!