I know Firaxis had problems with PBEMs and patches way back when they made PTW, but they seemed to have gotten better in C3C. My question is, can I install the patch and still play my current PBEMs with the new patch? Or do I need to make a mirror copy of Civ4 and Warlords to play with different builds? Thanks in advance.

Don't know about upgragin to warlords, but when i upgraded from 1.52 to 1.61 only thing i noticed that the game date(1100AD-->1300AD, or something like that) changed.

It is my understanding is that all the players have to be on the same patch.

I do not know how true that is, or what issues may arise (other than the players with the latest patch will get a "penalty" from the forrest chops)

I found out the answer. All existing games will have to continue under the old patch. They won't work with the new patch.

Yes, old version200 pbems, will not load for the new version208. I had to reinstall Warlords, copy and patch a mirror file.