Problem with OS Change 2K->Xp

Hi Folks!
My wondeful OpenGL terrain renderer worked perfectly with Win2K, but now I´ve installed WinXP and I´m encountering several problems. The textures don´t seem to work properly and and alpha-blending is just incorrect…
Has anybody had similar problems?? Please help, it´s really annoying!
P.S. I´m using VC++ 6 and have a GeForce256 DDR.