What version of Ruby is required for P4Ruby and where is P4Ruby installed?

I am trying to set up Ruby and P4Ruby so I can use the p4replicate.rb script, but whenever I run the p4ruby18.exe (from the Perforce FTP) I get the following error:

Perforce P4Ruby API for Ruby开发者_StackOverflow中文版 1.8 - InstallShield Wizard

There was a problem tying to get the P4Ruby install path.

Possible reasons are:

1) Ruby is not installed.

2) An unsupported version of Ruby is installed.

3) The folder containing the Ruby executable is not in the system path.

4) The folder of another version's executable is in the system path before the supported version.

5) The P4Ruby install paths are not writable.

OK

I'm running Windows Vista, and have Ruby 1.8.6-p398 installed in C:\Ruby186. The directory C:\Ruby186\bin is the first thing on my Path variable (the Ruby installer put it there)! I've also confirmed it's accessible by running which ruby (cygwin is installed) which returns /cygdrive/c/Ruby186/bin/ruby. I've tried 1.8.7-p334 and 1.9.2-p290 as well.

The P4Ruby release notes claim that Ruby 1.8 is supported for versions of P4Ruby 2007.3 onwards, so I thought I'd met this criteria but it will not install.

As I'm fairly certainly I've met criteria 1, 3 and 4, I wondered whether anyone could tell me if they've managed to install P4Ruby on Windows with a specific version of Ruby (2), and if so what path P4Ruby installs to (5)?

Just a sanity check: do you have admin rights when running the installer?

To answer my own specific questions (rather than solve my problem as thankfully @p4-randall did):

1. the p4rubynotes.txt manual says "The P4Ruby Windows installer requires Ruby 1.8."
2. P4Ruby is seemingly not installed anywhere! To clarify this, it looks like the P4 client is updated with a version supporting P4Ruby, so the directory it needs to write to is the Perforce installation directory (e.g. C:\program Files\Perforce\).