I personally would create two partitions for Windows whilst installing W7. A 250GB partition for Windows C drive (unless you plan on installing loads of games), and ~5000-600GB for Windows D (for personal files and data), and then leave around 50-100GB free at the end of the drive for Linux, but keep it unformatted.
Then when you install Linux, I recommend the following partitions:
10-20GB for Linux root / -- ext4 Primary partition
10-20GB for Linux user /usr -- ext4 Extended partition
~remainder of free space (min 10GB) leaving enough for below as /home -- ext4 Extended partition
Double RAM size in GB for SWAP -- So if you have 4GB RAM, create 8GB swap Extended partition
It is recommended you keep swap either at the very front of the disk, or at the very end to make access quick. Your first 3 partitions will be primary partitions, but the remaining 3 will be extended. This is because Linux can only handle either four primary partitions, or three primary, and a further 64 extended partitions.
Also, have a read of my step by step guide on
here, this will give you an insight into the process of installing Ubuntu, the Mint Linux installer from memory is fairly similar as the main Mint release is derived from Ubuntu.
You will be able to access both Windows partitions in Linux, therefore keeping all of your personal documents in the second Windows partition will in effect create a central location to access your data using either operating system. Windows is however, unable to read Linux partitions, so any data contained within your /home directory in Linux will not be readable in Windows.