Though the Opa compiler (as of this writing) doesn't have a 32-bit binary for Windows, I got it working in an easy way on (32-bit) Debian squeeze, after upgrading my nodejs installation.
Following Opa's instructions to install as a user (under the heading, Other Linux Distribution), I downloaded and ran their 32-bit Linux self-extracting package. When prompted, I chose to install it into ~/progra/mlstate-opa.
Then, after navigating to A tour of Opa in the sidebar, under the heading, Easy Workflow, I found and typed into a file, 'hello.opa' their sample program. The command:
$ opa hello.opa --
errored out, asking for more npm modules to be installed.
Rather than exactly following their suggested course of action, which would have installed node modules to root-owned directories, I typed:
$ npm install mongodb formidable nodemailer simplesmtp imap
After that the compiler worked just fine.
Copyright (c) 2012 Mark D. Blackwell.