Install a driver
If you want to install some driver in ReactOS you need at first the binary itself but also it's settings in the registry. This howto tells you how to accomplish that.
In an ideal situation, you'd need a PC emulator (Bochs will do, but VMware is faster), a copy of Windows NT 4 and ReactOS. Boot into Windows NT 4, open regedit, save the entire registry to a .reg file, then quit. Install the driver, restart if necessary, then open regedit and save the entire registry to a .reg file again - a different one this time. Compare the two either manually, or run them through DIFF. From this, you should find the settings needed by the driver.
You can then copy the driver over to your ReactOS system32\drivers folder, and add the necessary settings to the registry.
The registry is fairly straightforward. To edit it, you can either do so from within ReactOS itself (using regedit), or with a text editor. To do this, you'll most likely need the source code. Go into the bootdata folder, and open up hivesys.inf in Notepad or your favourite non-formatting text editor. For each driver (*.sys file) you want to test, just copy and paste an existing chunk from another driver, changing the type and start type as appropriate (eg: Video, Automatic...) - see the bit at the top for a list of the driver types.
Once you're done, run MKHIVE (in the tools\mkhive folder of the source tree) passing the bootdata folder as the first parameter, and the target folder as the second. In my case I have to do this: ..\..\TOOLS\MKHIVE\MKHIVE . V:\REGISTRY ... from the bootdata folder.