Hi:
There is a difference between "accessing an old mainframe database" and "accessing an old mainframe sequential file". For example, if you have an old mainframe IMS or DB2 or IDMS or Adabas or FOCUS database, then in order to read the data base directly with SAS, you would need the appropriate SAS/Access product for that specific database. If you have an old ISAM, BSAM or VSAM file, you may be able to read it with SAS. If you have sequential tape files, you may be able to read them with SAS.
You'll have to be a lot more specific about exactly what type of "old mainframe" file/database you're dealing with. Your description doesn't sound like a database (a collection of related tables) but more sounds like a single file or set of single files.
Is there no one at your company who remembers what this file or set of files was used for? No documentation? No data dictionary? No record layout stuck in an old dusty binder someplace?
At the very least, using IBM tools to look at the VTOC information in the catalog (assuming it's a cataloged dataset) should tell you things like the DCB characteristics: DSORG, RECFM, LRECL, BLKSIZE, etc. Using IBM JCL, you can also dump out the contents of a file in hex or in readable form (I don't remember the exact syntax for doing this -- but a good JCL book might help you there.) That's where I would start -- find out basic operating system information before I threw SAS at the problem.
This paper has some useful information on finding files on the mainframe:
http://www2.sas.com/proceedings/sugi28/001-28.pdf (Section 3, starts on page 7)
In addition, saying that you have SAS available isn't much help. What version of SAS do you have available: 6.09, 8.2, 9.1??? And, when you access SAS via a dumb terminal -- do you go into TSO, Wylbur, Roscoe?? Do you have ISPF available? How do you submit jobs? With JCL?
Your best bet for help may be to open a track with SAS Tech Support. There are really too many unknowns for someone to give you useful suggestions (in my opinion).
cynthia