There will be a solution in the next release apparently.
Until then the suggested work around is to go to directory:
c:\program files\IBM\sametime connect\plugins\com.ibm.collaboration.realtime.exchange.win32.x86_7.5.1.20070416
and rename:
OutlookJNI.dll
to something like
OldOutlookJN.dll
sametime 7.51 seems to start quicker as well now.