Looking through Synaptic, I noticed that I have "mepis-install" installed. That is described only as "installer for SimplyMEPIS," so I would guess that it's the installer that I used on the liveCD. Since I am never going to install MEPIS from the copy of it on my hard drive (I wouldn't know how, and where would I install the new copy?), can I safely uninstall mepis-install?

Have many versions of Mepis have you install ?
What output gives the command fdisk -l ?
How many options do you have at boot time CQ menu.lst ?
Which OS are you running now ?

In Synaptic there is a tab that lets you get a list of all files that are part of any installed package. It would be wise to examine that list before deciding to remove the package.

The description of that package might be misleading, so the list of files might tell you more.

I suspect it is safe to remove that package. I suspect it got installed as a side effect of the close relationship between the Mepis liveCD (which obviously needs the installer) and the initial Mepis installed system, which doesn't need it.

I suspect the only advantage to keeping it would be if you want to make your own customized Mepis liveCD based on the current state of your installed system. (The installer would then be used if you wanted to install your customized Mepis onto another system from you customized liveCD).

I suggested checking the file list in case I'm wrong about why the installer is still there.