I'm sorry that the OneCare undo apparently enabled the Windows Firewall. OneCare should enable it on an uninstall, but it seems that it is also doing this when an install is backed out.
You should be able to access the firewall policy by entering gpedit.msc in the Vista search box and then responding to the UAC prompt that comes up. Details beyond that I don't know.
My recommendation is to contact support for instructions on how to resolve this problem - http://help.live.com/help.aspx?project=onecarev2 - use the get more help link in the lower right corner.
-steve