It would be more accurate to say it won't do full hardware acceleration of HD video, but whether it'll work, playback at full framerate without stuttering, depends on how fast the CPU is at doing the decoding. A typical modern dual core processor can manage this.
Even so, since it won't do HD decoding, 6100 is a poor choice when the target is a HTPC... but if you had the parts already you might as well try it, lots of video players won't cause the GPU to do the decoding even if it supports HD decoding and IMO, using the video player you want is more important in the end.