The original (first) Series 3 Tivo is the one with the OLED display on the front.
And IIRC, there are no DIY upgrade solutions for a 2TB hard drive.
You can use a 2TB hard drive with WinMFS, but the S3 will not use all of the space.
If you want a true 2TB hard drive for the S3, you have to get one from DVR Dude or Weaknees.