Whoa, acronyms :) So according to this question you can have multiple SSL subdomains on one IP address as long as your server supports TLS (which Apache 2.2x does).
Another answer to that question points out that the client browser must have SNI support to work, which IE doesn't have on Windows XP. So, what happens to people with that browser is a warning message saying that the SSL cert doesn't match the domain.
Can one resolve this issue for those client browsers without SNI support? Does a wildcard (for subdomains) do the trick? Are there other (cheaper) options?