HELP!!! What RDBMS should I use?

Hi friend,

        I am going to use either windows NT 3.5 or UNIX (coherent) on a 486DX2/66, and also a RDBMS application developer to build my own real-time, multi-tasking application that will be getting data from two VT100-type (WYSE) terminals that will be connected to the main PC with serial or parallel ports, so I can create a Point Of Sales system(POS) that will be also using five printers individually (real-time, multi-task).

        Should I go with windows NT or UNIX, and what RDBMS supports multi-tasking on VT100 terminals through serial or paraller ports?

P.S: Have in mind that I can only spend up to $5000 for the whole system.

                                        Are you experienced with that?
                                        Please e-mail or post here.


                                        Nikolas Spyridonos