This post from Doom9 (http://forum.doom9.org/showthread.php?t=101353) has a download for a different version of DGDecode 1.1.0 that's faster than the original version (ie the one that comes with the installer). Currently you have to have an SSE2 capable CPU (P4 or A64) right now, but NaN (author of NanDub IIRC) is working on an SSE version. I haven't tested it yet but it appears to be worth a look.
The SSE1 version has been released now! Direct Download link: http://forum.doom9.org/attachment.php?s=ab8e924aff4da8abbb05a85db8875da4&attachmentid=4807 Original thread: http://forum.doom9.org/showthread.php?t=101353