Finally unplugged the 24-inch alum iMac and put in the new RAM, which has been sitting on my desk since, oh, about 2 days after I got the iMac which was about 3 days after they were announced.
What a difference. Word (even the new 2008 version) still seems to take a while to open up, but everything else seems to be going much, much more quickly.
Sure wish I'd bit the bullet and done it back in August! Or, since I didn't do it then, I wish I'd bought RAM when it was cheaper.
Oh well. Over. Done with. My machine seems like a new baby now.