Hi Werner,
Yes the HELP engine as been replaced in TD 5.1 and the reason was to address the issue of VISTA no longer supporting the OLD WINHLP32 engine( though this can be workaround in VISTA). So in effect there is no longer SQLWIN.HLP provided in TD 5.1 but HTML file instead. This system currently does not support context sensitive help

and as you point out, F1 in the context, still try to look at for SQLWIN.HPL. If you would have one SQLWIN.HPL (from previous TD version) along in your your system path both HELP would open... We are aware of those 2 issues and look at currently at it.
Originally Trial version could not be patched (applying PTF to it), I would believe this rule did not change, unless someone state otherwise...
Thanks
Jean-Marc