Try the x86_64 build from here:

http://releases.mozilla.org/pub/mozilla.org/xulrunner/releases/2.0rc1/runtimes/

You'll have to do manual GRE registration to put a necessary file in your ~/.gre.d/

$ cd xulrunner
$ ./xulrunner --register-user

You might also temporarily remove the file /etc/gre.d/2.0.system.conf to ensure that the run-conkeror
script (which is in conkeror's contrib/ dir) will definitely use the right version.