Regardless of the darkness of the paneling, there are a few preperations that you will have to make before painting the panels. I would first suggest cleaning with TSP (kinda like a clorox) but stronger. This will just get the dirt and the grime off of the paneling Then I would suggest putting "deglosser" on the paneling. This removes the "shine" from paneled walls. Depending on the results of your "deglossing", you may or may not have to do some sanding. Remember, sanding never does anything but make a paint job better. So it's an option I would consider. Even if just light sanding. Next, you will need to paint a base coat of "primer" on the paneling. This could be an enamel undercoater or an actual stainblocker like "Klitz" (Open the windows and doors if you use this stuff) Get your local paint store (where painting contractors go...not wal-mart or K-mart) to recommend a primer. Once primed, you are ready for your first coat. BTW, I assumed that this paneling was stained and sealed and not just painted dark. If the later is the case, just prime and paint Someone else may have a better way to do this...but this is the way that I have done this in some past DIY remodeling projects.