I'm running a 550 and software decoding takes less than 50% CPU usage with WinDVD 1.2.99 (no hardware assitance in that)
You will be fine..get PowerDVD 2.55 or WinDVD2000 IMO they both look nicer than a hardware DVD card.
The hardware DVD card has nice TV-output..but that's about it, for a monitor playback software is good, and the stupid passthrough cable won't mangle your 2D.
Just get a GF2 with TV-out and you're good to go.