Except for its lack of HD video output--and lower price tag--the Roku SD Player is otherwise identical to its step-up sibling.
The Roku SD Player is the entry-level model in Roku's line of streaming media boxes. The "SD" stands for "standard definition"--it's the only one of the three that has no HD video or digital audio outputs. The price is $80--which is 20 percent less than the otherwise identical Roku HD Player.
We haven't reviewed the Roku SD Player, but the review of the HD Player should give you a good idea of how it will perform (with the obvious caveat that video quality will be limited to standard-definition). However, we'd recommend springing for the extra $20 and buying the Roku HD Player instead--even for those who don't plan on connecting the Roku to an HDTV in the short term. That's because you'll almost certainly be upgrading that old TV to an HD model in the next few years, so you might as well prepare for that likely eventuality.
Read the CNET review of the Roku HD Player