The recently released Google Drive doesn't have a built-in capability to assign a drive letter (i.e. F:) to it's content, so people will be able to access the Drive using "My Computer" on Windows based machines.
In fact, thanks to old friend - the "substs" command from MS-DOS times, it's very easy to fix. This command-line utility exists since MS-DOS era (20 years ago!) and it's still included and works in Windows XP, Windows Vista and Windows 7 machines.
subst [drive1: Path]
Real-life Windows XP based example:
subst f: "C:\Documents and Settings\Vadim Solovey\My Documents\Google Drive"
That's all it takes, really. Go to your My Computer, you'll see a new drive letter (F: in my example) pointing to your Google Drive's content.
You can run subst command without parameters to see what drive letters are assigned to what paths. As well, the /d parameter deleted a drive letter (it doesn't touch the content of your Google Drive, off course).
If you really hate messing with command line, you can use Visual Subst which does the same thing exactly (actually, it's a GUI which runs the same subst command under the hood).
IMPORTANT - The subst will work until you restart your PC. After the restart, the drive letter will disappear. You'll need to create a .cmd file with your subst command and put it in to the startup folder of your Windows installation to re-create it each time you're restarting.