BP7 Dos application running under NT

We have a BP7 Dos application that works fine under Dos and Windows95 that
uses self written screen painter, serial comms routines and graphics.
When we launch our application under NT, starting up the apllication,
screen swapping and graphics take up a lot of time and serial communication
doesn't work properly.
Who has experience wit BP7 Dos application running under NT and can suggest
me a screen painter, serial communications library and a graphics library?

Thanks,
Peter