Ah, commerce and currency; the very fountainhead of all Crystal Reports! I suppose it is very well that Crystal allows us to format pretty much any numerical value to a "Currency" format. To do this;
Any numeric field can be formatted as "currency" by:
1. Right-click on the field itself
2. Select "Format Field"
3. Go to the "Common" tab
4. Select your Style (i.e. thousands seperator, etc)
5. Click the checkbox labeled "Display Currency Symbol"
ProTip: This does not change the Data Type! It simply controls the formatting of the numerical value provided.