to the best of my knowledge, you can't have different formatting options (i.e. some words in bold, others in italics, etc.) within a single <text> element. BTW, this is a rather general limitation found in basically every experimental package (E-Prime, SuperLab, etc.). With that said, here are a few workaround strategies:
(1) Use multiple <text> elements and align them properly. However, this is a tedious strategy if you're dealing with long segments of text that require a pretty complex layout.
(2) Prepare the text with all the desired formatting in your favorite word processor (OpenOffice Writer, MS Word, AbiWord, etc.). Then make a screenshot / export the text as a picture file and use Inquisit's <picture> element to display it.
(3) If you want to display nicely formatted text on an instruction page, use Inquisit's <htmlpage> element rather than the standard <page> element. Again, prepare your text with a word processor of your choosing and then export it to HTML (all major word processors have built-in support for this).
Hope this helps,