We had a player leave our PBEM game and he didn't pass on the password. How do I open his save to continue the game? Any suggestions?

The administrator should be able to do this by using the administrator password instead. Then changing it in Options.

... and if the admin either didn't set a password, or forgot it? Is there a default admin password that gets used?

then, you're stuffed, I believe...

..unless there are technical geniuses around who can hack this..

but if so, i don't know who they are..

We had a player leave our PBEM game and he didn't pass on the password. How do I open his save to continue the game? Any suggestions?

I would suggest that you try the saveconvert program, that you can
find here at civfanatics.com:

1/ First hand, try again to get the password, so you do not need the saveconvert program.

2/ Get the savefile from someone that has done everything in her/his
move without finishing it. You need also the savefile from that person.
If needed, go back in game-time and take the savefile that you got
yourself (I assume that you are yourself in the game) last time and
make your move without finishing it. Save the game in a new file at
this point, before hitting enter.

3/ Put this new savefile with a simple name in a folder on your
computer and put the saveconvert file in the same folder.

4/ Use the saveconvert program to change all human players to
AI players, except yourself (or the person that you got the savefile
from) of course. Change the game mode to Hotseat. Save the
result as another file and test to run it in Hotseat mode, to see if
everything looks alright.

5/ If it is OK, use the saveconvert program once again to change
back from human to AI the same countries you changed earlier. Change
game mode to PBEM and save to a new savefile. (Another way is to
save it as Hotseat and open it in Civ4 as PBEM.)

6/ I hope that the passwords now has disappeared and that everyone
can put them back when the turn goes around as usual.

Please note that this is just a suggestion on something that you
might try. I do not know if it works and give no guarantees. It
all depends on the saveconvert program working correctly and on
that the passwords really disappear when you change from human
to AI. Perhaps they are still kept and later reused, and in that case
this suggestion would not solve your problem.

Good luck!
-- Stormumriken

Nope - that didn't work. The password persisted. However, using the savegame convert program does mean that I can change that non-playing player to an AI and we can continue the game.