Rails install w/ multiple servers has vague question

Almost finished installation of Ruby/Rails on webappX, as per this

Since the Rails procedure requires it, I also had to install all the
MySQL 5 packages incl. devel on both webappX - but of course disabled
mysqld from starting since we want it to talk to the instance on
mysql0. Very close to the end I hit what is probably a minor snag.
Rather than guess at the answer, I thought we would ask the experts

The document says this:

gem install mysql -- --with-mysql-config=/usr/bin/mysql_config
    Select option 1 - mysql 2.7.1 (ruby)

And here's what I saw when running it:

[root@webapp0 ~]# gem install mysql -- --with-mysql-config=/usr/bin/
Select which gem to install for your platform (i386-linux)
1. mysql 2.7.3 (mswin32)
2. mysql 2.7.1 (mswin32)
3. mysql 2.7 (ruby)
4. mysql 2.6 (ruby)
5. mysql 2.5.1 (ruby)
6. Cancel installation

Which one should I select? What's with the mswin32? Using CentOS 4.4
(same as RHEL 4 Update 4)
and MySQL 5.