Please be more specific on what it is that you are trying to install as there two types of "GB" you could be installing.
About 2.1 Gb on a fresh install.
Depends what you install.
Windows 7 required 20 Gigabyte (GB) of space to install a 64-bit version into the system.
You will need approximately 15 Gigabytes (GB) to install World of Warcraft.
Yes, you can.
about 2 GB
1 GB recommended
No, it requires a min of 16GB.
8 gigabytes
When you install WoW, it install all expansions and patches up to the current client. This is even true if you do not upgrade your account to BC or Wrath. So it will take about 15 gigabytes.
60 GB, although with a windows install that goes down to 52.8GB
6.0 free gigabytes (GB) plus the base Spore's minimium memory.