As I suppose this is display driver. There are WDDM - windows display driver model. WDDM is very changed since Vista (before its called XDDM) - major change - display drivers now are usermode dll. You must perform 4 steps for success:
1) Read about windows xp XDDM : http://msdn.microsoft.com/en-us/library/windows/hardware/ff570584(v=vs.85).aspx / Here you must also perform sanity check on driver - check that it`s XDDM driver - look at exports, inf file, etc
2) Disassemble driver with IDA for example (maybe you can just disasm how driver work with hardware or not)
3) Read about windows Vista WDDM : http://msdn.microsoft.com/en-us/library/windows/hardware/ff570593(v=vs.85).aspx
4) Rewrite driver to WDDM