VI and pre-VI saves

[Thon]

i'm finally giving in and picking up VI.

i was wondering however, if i installed it would all of my current save games no longer be playable?

[Count Fudgula]

As far as I know, save games of different versions are completely incompatible with each other. So you'd better finish off that campaign before installing any new bits like VI.

Don't know about replay files though...

[Gregoshi]

The good Count is right - game saves between MTW and VI are incompatible. I think maybe replays are too. Anyway, when you go to install VI, you will get a warning message box about this incompatibility right at the beginning.

[Brutal DLX]

Not entirely, most save games fail to load and will lead to crashes to desktop, some produce a blank black screen that might be convertible to a functioning, albeit a little unstable campaign by hitting Esc to bring up the in game menu and then clicking on resume game, and some may even load without problems, but might or might not crash later on.
So, the majority of save games will not work and it's better to finish your campaign first before moving on to VI.
The replays, you can still watch by renaming their file extensions, however some odd things may occur that can lead to different outcomes than the actual one, but that problem is more prominent when viewing VI 2.00 replays with the 2.01 patch installed, in which case you would need to swap the TW.exe.