If you are using Hackman, the 8.x release introduced a low file size limit in the freeware version (so it only opens the first 200KB or something), making it useless for editing the data.000 file. It is still possible to find the previous 7.x release, though; check
here, or search
Google for "hack704.zip" or "hack702.zip", etc.
Alternately, you can use a different hex editor, such as the freeware programs
Frhed,
XVI32 or those listed
here or reviewed on
this site.