If you are proxying Subversion through Apache, chances are you are probably using a non-default port since Apache won't start if you configure it use port 80 and 443 for SSL if you have IIS installed.  IIS uses socket pooling which binds port 80 and 443 on all IPs -- even ones not use by IIS -- to IIS.

To disable this behavior, you need the httpcfg.exe utility.  For Windows Server 2003, this can be found in the SP1 32-bit Support Tools download.  For Windows XP, the utility is available as part of the SP2 Support Tools download.

You can find a good overview of how to use this tool at neowin.net.

Some tips:

• I didn't have luck running net stop http /y alone; I had to stop IIS first by running net stop iisadmin.
• Assuming you have two or more IPs, the key is that you are actually telling IIS which IPs are okay to bind to.  If you are proxying Apache over IIS, you are likely (or should) use SSL.  This means that you have to make sure that you explicitly force IIS to bind to 80 and 443 for a specific IP and leave the other IP available for Apache.