Vista - restoring previous versions BEFORE A CORRUPTION occurred to PST fi

I have had this same problem 3 times since gettin Vista in Feb 2007...somehow
my Outlook and attached pst file get corrupted and then Outlook and that pst
file become un-openable, un-useable, etc. Twice I have had tech people
unistall entire Office 2007 and reinstall the Vista operatin systems and then
reinstall Office 2007 to get things to work again. Problem is the pst file
cannot be repaired as is. We have tried nearly everything but the tech guys
say since the root pst file started at Office 200, they cannot repiatr the
file..SO, we have been trying to restore the pst file from an earlier
version...which has been effective BUT now I think made a HUGE mistake...I
use Windows LiveCare/OneCare and have the system protection and automatic
restore points turned on...SO, I discovered accidentally that I could
"restore to previous verions" and did so to my corrupted pst file.....PROBLEM
is I think I restored to the previous version that was right after the
corruption (7/17 5:49PM) versus the last version before the corruption (7/17
12:30AM)....then I left matters alone and did not yet reinstall Office 2007
etc. due to travleing and just now geting back to trying to fix
everything...(have been using webmail in mean time)...I woke up in middle of
night last night and tried to restore to previous verion 7/17 12:30AM....Also
I cannot find any previous other versions now prior to 7/17 5:49PM...so is
there a way to RECOVER those previos versions??????? of pst files that were
saved or shaow-copied BEFORE the corruption which ovccurred arond 5 PM
7/17...?