X11R4 problems

[Geraldo Veiga]

Is it possible to run client a linked with the X11R4 libraries under an
X11R3 server?

I have started playing with the X386 distribution, and tried to run the
client binaries under an old ISC X server (version 1.0).  Without fail,
I get the message:

Error: Can't Open display

I have the R4 shared libraries installed. 

At the moment, I lack the appropriate hardware to run the X386 server.
Also, I'd to know if it is possible to exchange X client binaries
across 386 platforms.