I started feeling guilty after sending you on a bit of a wild goose chase with the results of my Google searches, so I thought I'd try it myself. I created a site in the root of my 64-bit test server, which lives at 192.168.1.103. Then I went to my 32-bit dev server, which is at 192.168.1.3, and did the following:
First I installed the package
Then I enabled the three (3) mods
sudo apt-get install libapache2-mod-proxy-html
Then I edited the '/etc/apache2/sites-available/default' file and added the following two (2) lines immediately after the DocumentRoot directive
sudo a2enmod proxy proxy_html proxy_http
Then I restarted apache2
ProxyPass /u64/ http://192.168.1.103/
ProxyPassReverse /u64/ http://192.168.1.103/
Now when I browse to...
sudo service apache2 restart
...I get exactly the same site as if I browse to...
The links are all mapped and everything seems to be working as it should.