windows 7 - How small can/should I make my partitions, on a dual boot with a shared middle drive?

My machine is currently split into 3 user partitions (plus however many Windows and Linux have decided to slyly create) Which are C: Windows 7, D: Data, and E(?): Ubuntu. I'm considering wiping my Windows 7 Install (stupid Skyrim not installing) and restructuring the way my machine operates.

I want the partitions for the Windows and Linux install to be as small as possible while still able to function well, and be able to install games on my Windows C: drive. I then want to link from both Win7 and Linux drives to the middle D drive so that the in built My Documents (and etc on windows) folder and my Home folder (linux) share a common location, rather than my current situation which is 3 separate file locations.

Something like this:

I have 1 TB to play with and I want to know the 'best' sizes to make these partitions when I reinstall Windows (which I need to do anyway) and re-jig everything.

This massively depends on the games you will install on C:\ and the applications you will install under Linux.

Moreover, Windows tends to accumulate additional fluff over times (downloaded patches, service packs etc.). Linux does this, too, but usually to a lesser extend. A partition that is "just big enough" today can become awkwardly cramped over time.

The general rule of thumb is: Make the partitions bigger than you need 'em. Resizing partitions on an already cramped system is a major pain, and risky too. Better have enough space for the operating systems right from the start.

Because, if you run out of space for data, you can just plug in a second hard drive.

Edit: The most useful dual-boot setup I have found so far is to have the "data" partition formatted as ext3fs, mounted as /home/username under Linux, and using ext2fsd under Windows. I found that to be more transparent and comfortable than working with data on a NTFS partition under Linux. Then again, I'm primarily a Linux user, so your mileage may vary.