You can open installed fonts directly from FontCreator. There are for TTF files for Times New Roman.
If you’re creating your own fonts you need to create a new TTF for Italics, and another one for Bold. You also need to change some font settings so that Windows can correctly identify the font style.
This Old Post in the FAQ might be helpful to you, since you’re using an old version of FontCreator. More recent versions can automate the process of changing the font settings.