There's no prebuilt way to do it, but setting it up yourself is pretty simple. Here's a way to do it in three short events:
It's mostly straightforward, except for the mid() function if you're unfamiliar with it. Its function is to take a smaller part out of a whole string. It takes three parameters, a text variable (or the string itself, if you want) that you want to display, the letter you want to start on, and how many letters from there you want to go.
So the way I wrote it is, the variable TextCount is incremented once a tick. Every time it's divisible by 5 (which happens twelve times a second), use the mid function. It looks like mid(Cake,0,(TextCount/5)), so let's break that down.
Cake is the text variable I made, which says "This cake is delicious!" (yum! <img src="smileys/smiley4.gif" border="0" align="middle" />) 0 is the letter you want to start on, which is the first one, "T". TextCount/5 is how long you want it to go on for -- since TextCount is divisble by 5 every time the function is used, that'll always be a whole number. When TextCount is 5, TextCount/5 is 1, so mid is taking the substring of Cake from letters 0 to 1, which only includes "T". Once TextCount is 10, TextCount/5 is 2, so mid takes 0 to 2, which is "Th". It keeps going on until the entire string is displayed piece by piece.
Hopefully this is what you're looking for and hopefully my explanation was good enough. <img src="smileys/smiley1.gif" border="0" align="middle" />