Yes it will. Set it up last night as my default voice, and now it is just that. I did not run or load Text Aloud (cute program) on this boot and was able to read text from a MS "Works" document.
Update,
I just moved Heather to my HS machine without installing TA and it works as a system default. It comes up listed as a "HQ TTS English" engine. I did (like someone else) get a firewall request to connect to Acapela, I declined the connect this time and everything appears to be fine.