NT and internal modems

I installed nt and sp6a on a clone pc with brand name components. The modem is an internal us robotics 56k. I tried to install the modem but nt does not recognise it. I checked for IRQ conficts and memory conflicts and there some issues with the memory allocation on the com1. I tried using new drivers but no luck.
I always have trouble installing internal modems, externals are no problems.
I hear that installing additional ISA drivers from the NT installation cd helps?
Any ideas?