Usually it is as simple as: download, install, run. You can run into problems however if you have both the 32 bit and 64 bit JVMs installed (which is quite often) because it will try to use the 32 bit JVM. You can check which JVM is being used from the command line:
jruby --version jruby 1.6.3 (ruby-1.8.7-p330) (2011-07-07 965162f) (Java HotSpot(TM) 64-Bit Server VM 1.7.0) [Windows 7-amd64-java] # 64 bit jruby 1.6.3 (ruby-1.8.7-p330) (2011-07-07 965162f) (Java HotSpot(TM) Client VM 1.6.0_26) [Windows 7-x86-java] # 32 bit
To work around this issue, specify the JVM to use in your jruby.bat (or other batch files installed by gems like vagrant.bat) explicitly. Example jruby.bat:
@ECHO OFF java -Djruby.home=C:jruby-1.6.3 -jar -jar "C:jruby-1.6.3libjruby.jar" %1 %2 %3 %4 %5 %6 %7 %8 %9
Example vagrant.bat
@ECHO OFF java -Djruby.home=C:jruby-1.6.3 -jar "C:jruby-1.6.3libjruby.jar" "C:/jruby-1.6.3/bin/vagrant" %1 %2 %3 %4 %5 %6 %7 %8 %9