Harddrives are already formatted when you get them (physical format, not logical format) but some people (including drive manufacturers) will talk about 4.2GB = 4,200,000,000 bytes while others will talk about 4.0GB = (the limit of 32-bit addressing) = 4,294,967,296 bytes
And yes, the 4GB limitation does not mean that you need a drive of 4GB or less, you just won't be able to use the additional space.
