Thank you - in the meentime I found this http://www.der-eremit.de/post/13589628448/ssl-enabled-name-based-virtual-hosts-with-mod-gnutls but I think it is outdated...
– PatrickDec 04 '13 at 16:58
If the xp client is using IE then it looks like no. If they use chrome/firefox etc then it will work. http://stackoverflow.com/questions/5154596/is-ssl-sni-actually-used-and-supported-in-browsers
– Russ HuguleyDec 04 '13 at 19:03