hybrid website? php and rails..

i am writing a new app in rails that i need to run on an existing
domain..

the problem is, there are a few subdirectories on that domain that run a
few old (but necessary) php scripts and a few other things that still
need to be accessible..

is it possible to set up apache so that i can run my rails app using
mod-proxy, but still retain access to the old directories in
~/public_html ?

Yes.

the only thing i would do is make sure that there is no directory name
overlap in the system..

for example.. i couldn't have /scripts in both apps.. which is fine..

i would appreciate any help in getting this set up..

This is what we use and it works fine. (apache2/mongrel)

<VirtualHost *:80>

    ServerName myserver.com
    DocumentRoot /path/to/my/app/public

    <Directory "/path/to/my/app/public">
      Options FollowSymLinks
      AllowOverride None
      Order allow,deny
      Allow from all
    </Directory>

    <Proxy balancer://mongrel_cluster>
      BalancerMember http://127.0.0.1:8805
    </Proxy>

    RewriteEngine On

    RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} -d
    RewriteRule ^(.+[^/])$ $1/ [R]

    RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} \.php
    RewriteRule ^(.*)$ $1 [QSA,L]

    RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
    RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME}/index.html -f
    RewriteRule ^(.*)$ $1/index.html [QSA,L]

    RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
    RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME}/index.php -f
    RewriteRule ^(.*)$ $1/index.php [QSA,L]

    RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} -d
    RewriteRule ^(.*)[^/]$ $1/ [QSA,L]

    RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
    RewriteRule ^/(.*)$ balancer://mongrel_cluster%{REQUEST_URI} [P,QSA,L]

    AddOutputFilterByType DEFLATE text/html
    AddOutputFilterByType DEFLATE application/x-javascript
    AddOutputFilterByType DEFLATE text/css
    AddOutputFilterByType DEFLATE text/plain
    AddOutputFilterByType DEFLATE text/xml
    AddOutputFilterByType DEFLATE application/xml
    AddOutputFilterByType DEFLATE application/xhtml+xml

    BrowserMatch ^Mozilla/4 gzip-only-text/html
    BrowserMatch ^Mozilla/4.0[678] no-gzip
    BrowserMatch bMSIE !no-gzip !gzip-only-text/html

    php_value include_path /path/to/my/app/php:/usr/local/lib/php:.
    php_value auto_prepend_file /path/to/my/app/php/auto_prepend.php

    # this not only blocks access to .svn directories, but makes it appear
    # as though they aren't even there, not just that they are forbidden
    <DirectoryMatch "^/.*/\.svn/">
      ErrorDocument 403 /404.html
      Order allow,deny
      Deny from all
      Satisfy All
    </DirectoryMatch>

</VirtualHost>