acts_as_taggable_on won’t allow you to add tags on create. You can save it twice, but that makes the controllers ugly. Ideas for fixing it include adding a wrapper class that abstracts the double-save, or writing your own unless you really need all the features of acts_as_taggable_on.
jQuery 1.6.2 crashes and burns in IE8 in incompatibility mode. Upgrade jQuery to fix it. jQuery 1.6.4 is out recently, so upgrading shouldn’t be a problem.