General wisdom is to finish projects in the version you started with, so yes.
Even if you do install CS5 on the new system, you still will not have the correct fonts for your project. Fonts are controlled by Windows, not PPro.
The easiest way I've found to correct this is to open the project, then open the Events window, then note which fonts are missing. Close the project (without saving), install the needed fonts and you will be good to go.
Thank you so much, gentlemen.
I ended up importing the fonts and, while it didn't automatically change
them back, I was easily able to change them (though for some reason my
title, created in FuturaLT, seems a tad bolder than it did before).
Now having issues getting 6.0 set up to export an AJA Quicktime (was much
easier to figure out what to download in 5.0), but that's another post...