100MB is actually rather small compared to some of my files.  I usually use "Save Internally" since i am not concerned with save time or file size.  I only try for speed and low size if it is something I plan to sell.  I have two Poser runtimes.  The first is my old Poser 7 Runtime, and the second is the Poser 8 one.  I have them both set up in Carrara.  The poser 7 one has all of my older content, and the Poser 8 one is where new stuff gets put.   A defrag might help.   But Windows 7 does a pretty good job of reducing fragmentation on its own.  I would look for other applications or TSRs that stay running in the background and do a lot of things that increase HD activity.  I have had some files that can take over 5 minutes to load, depending on what is in them.