Nope, that's normal. There is a difference in how HDD manufacturers define 1gig of data, vs how a computer does. You could get 100 drives, and they'll all do that.
When you format a drive (a required step), some of the configuration for the hard drive is kept in an area on the hard drive. So you will always lose some space.
Before somebody corrects me, I tried to put that into very general and laymans terms. Whoever chimes in and shows off their talent of explaining that 22GB to explicit detail will get slapped.
320GB = 320070287360B = 312568640KB = 305242.8125MB = 298.08GB. Windows divides by 1024 to calculate Bytes/Megabytes/etc (which it should).
It's because of this conversion of bytes -> kilobytes -> megabytes -> gigabytes that you lose some space, also you can blame everyone else for incorrectly using SI unit prefixes. GB is 1000MB, as opposed to a GiB which is 1024, you can't blame HDD manufacturers.
you cant just magically delete a folder on the drive to fix it. thats just the way it goes. a lot of people arnt happy about this (including me. i have 465gb on my 500gb drive), and some people have seriously complained, but its just the way it goes.