Hey Mario.
I am doing something similar. If users do not have Infopath it will open in the browser automatically. IPFS does this check by default.
You can add an option to the URL to force it.
http://site/_layouts/formserver.asmx?XsnLocation=http://site/FormTemplates/template.xsn&OpenIn=browser
That would typically be placed in a field that was consumed by a hyperlink control.