General hints for unpacking .tar_lzw files on VMS:

1. use 
LZDCM -B file.tar_lzw file.tar

2. Use a utility like FILE to reset the "file.tar" file to
FIXED recordlength 512 byte files.

3. Assign this file to TAPE

4. Use TARRDR to unpack it all into a VMS directory tree.