Hi Juliana-
I would not use a free font for commercial use unless you clearly understand that it can be used for commercial use.
There are a lot of clones floating around that don't even have the <company name> filled out on the actual font file- I would steer clear of those!
It definitely is more difficult to find free script fonts that can be used for commercial use- probably because they take a LOT more time to design- LOL!
I am not sure about the fonts that come with computer programs- the terms of use are usually quite vague- so it wouldn't hurt to write to them to ask.
It definitely would be a good idea to buy a few fonts. I know many people think that $10- $20 is expensive, but it's really not- considering you get to use it over and over and over. The $2 scrapbooking fonts are usually just for personal use- some allow you to pay more for a commercial license.
Here are some gorgeous bestselling script fonts that average $12-20:
http://www.myfonts.com/browse/keyword/script/
Here are some very fancy script fonts by ES Typography that are "...free for all use and distribution..." according to the font files (no read-me files are included)
http://freefonts.fateback.com/es_typography/
HTH
