Serving multiple ssl certificates requires SNI on server and also client support.
http://www.rackspace.com/knowledge_center/article/serving-secure-sites-with-...
this works on Centos 6 without messing up openssl libraries :)
Take a look at this freeIPA how to I wrote a while back...
http://freeipa.org/page/Apache_SNI_With_Kerberos
Windows XP does not support SNI on its internal libraries (so no IE on that) and I'm not 100% sure when MacOSX enabled it.
It worked for subversion but not with older svnkit bindings so do some testing and ensure that all the clients you expect will support SNI ...
For me it was an interesting experiment (wiki, svn, etc on same IP) but they drawbacks out weighed the benefits when I opened it up to the developers to use so switched back to sperate IPs.