Or, you could import some letter models from Daz Studio via the Bridge - there are some free ready made letters and numbers  here at Renderosity:

http://www.renderosity.com/mod/freestuff/search.php?section_id=-1&query=letters&sort=relevancy&use_age=no&older_age=&older_units=day&newer_age=&newer_units=day&username=&section_selector%5B0%5D=-1

If you have Daz Studio (it's free)  just install them into into it, then load them into Bryce using the Daz Studio link.  It would be the quickest way to get some letters but bear in mind using letter objects will increase your render time compared to the other suggestions given. Just shout if you need any help with any of that:)

Beginners tutorials for Bryce

Bryce Arena