Several times, I have tried to install or upgrade something, and had Synaptic say that some number of programs that seem completely unrelated will be removed. The latest time just happened: I found the latest Pidgin (or a recent one, anyway) in the Sid repositories, and tried to download it. (Without this, I'll have to compile it from sources.) Synaptic says that to install Pidgin, several dozen items, including mepis-system and mepis-user, will be removed. ?! In other words, installing Pidgin would destroy my system. Can anyone explain this?

Did you look closer at what mepis-system and mepis-user are? Sometimes it looks like important things will be removed, but they are just metapackages, i.e. a single package name that really installs a group of other packages. If you remove a key component of KDE for example, it will remove the kde metapackage, but doesn't actually remove any other KDE programs.

I'll look again, but unless it's obvious even to my novice's understanding that they are only metapackages, I won't risk it. I already had to reinstall MEPIS once today, after an attempt to upgrade using the sid repository ruined the system by uninstalling important things. Even as fast as MEPIS installs, I can't keep disrupting my operating system--I'm in online graduate courses.

pidgin 2.5.9 is in lenny-backports, so if its recent enough for you (sid is 2.6.1):
if mepis is based on debian-lenny/stable ? it should work better.

(you could also try running "aptitude --keep-all", but as i aint got meta-packages i`m not sure on that)

Thank you, J1. That worked perfectly. I didn't know there was a repository called debian-backports.

good.
if you wannna know a bit more, here is the web-page:
http://www.backports.org/dokuwiki/doku.php
including a search-mashine for backports-packages.
Lets say its the official unoffial one :-)

i wouldnt mix stable with testing and or unstable, but others do so (that is: i aint got strong feelings on the matter).

(you could check for antix, which is mepis-based (with fluxbox and icewm) but may be upgraded to squeeze or sid if in desperate need one day. say as a dual-boot :-))
greetings

If you are using MEPIS, then use the Mepis community repos for backports and do not download from unstable/sid unless you really know what you are doing.