That red line you describe shown in My Computer means that there is less than 10% space available (or whatever your low disk space setting is set to.)
Have a look in Disc Management to see if that is actually your system drive, if so it will contain the boot files and mbr. Windows 7 creates this on install unless told otherwise. Unless you have set Windows to unhide system files then they would be hidden and explain why you not seeing them.
Sorry but can't answer your main question as its not something I have ever needed to look for.