The NT4 kernel contained most of what is known as WDM (win2k is just NT5 and XP is NT5.1). Almost everything except the plug and play stuff in fact. You can still use the old NT4 API, it is still there, your driver might fail WHQL though as some of these calls are 'disallowed' these days. The cals in question are the ones that access the hardware, these days it is supposed to be done through one of the system bus drivers. However, you can still wirte your own bus driver, we do, and still pass WHQL, so it is a little murky in this respect. Also, 2k and XP (NT 5 and 5.1) still run NT4 drivers, so you will have no problem if you use the NT4 DDK to write the driver. If the device is a network device, and you just stick to using the NDIS api, then it will run on CE (and linux too as there is an NDIS wrapper for linux). If you need to call any of the standard API funcs though your driver will not run on CE. Windows 98 supports a subset of WDM. What sort of device is it, because it is fairly straight forward to write a monolithic (hardware to IO manager) driver of the ISA bus on NT4. Nunc est bibendum!