InfoPath forms are rendered very differently than the standard list forms and the functions in SPServices aren't built to work with InfoPath forms.
I have a blog post about a very hacky way to do this with SPServices and jQueryUI, but you'll have to dig into the markup to make it work:
http://sympmarc.com/2011/08/24/using-spservices-with-jqueryuis-autocomplete-function-on-infopath-forms-in-sharepoint/
M.
I have a blog post about a very hacky way to do this with SPServices and jQueryUI, but you'll have to dig into the markup to make it work:
http://sympmarc.com/2011/08/24/using-spservices-with-jqueryuis-autocomplete-function-on-infopath-forms-in-sharepoint/
M.