An interesting idea . . .
First thing to consider is that the majority of land on Earth referred to as desert is not covered by sand dunes. Bare rock, compacted gravel and stone, salt flats, and so forth make up significant areas of desert surface on this world. Most sandy deserts are the results of weathering of specific regions of eroded stone, and the sand that results is often the color of said stone. Thus there are deserts with red sand, yellow sand, white sand, and even black sand. While I cannot think of any off hand, I imagine that there are places with brown or gray sand as well.
Furthermore, the defining issue of the desert is the utter lack of moisture upon the surface. This leads to several things: significant wind erosion rather than water (leading to a starker, rougher look to the terrain), a lack of vegetation (leading to stronger winds over the landscape, as no forests exist to slow them), greater differences in day / night temperatures (day might be 100*F, while night might be close to 20*F - even in the summer). However, note that water might still exist well beneath the surface. Indeed, oasis are regions where the land and sand / sediment is low enough that water beneath the surface is revealed upon the surface. If you have an underworld - or underdark as it is sometimes called - then the lower and more stable temperature, combined with the fact that rivers and even lakes might exist there - would likely make it a major strategic region, even for humans.
Note that rivers can still flow for significant distances through a desert. Consider the Nile, for example. Thus you might have a major river running from the equator-side of the continent towards the pole-side of the continent. Along the river - at least nearer the sea - will be a significant region for planting and either city-states or kingdoms. The difference will be determined by the stability of the flooding. If it is regular it will likely give rise to kingdoms, such as the Lower and Upper Kingdoms of Egypt, whereas if it is irregular in its flooding the situation is less stable, and city-states are perhaps more likely to develop.
The river might also run under the ground, erupting from the side of a cliff or out of an oasis at some point - seemingly from nowhere (unless towns exist under the surface along said river's underground length).
One perhaps notable consideration - just how large *is* the continent? Theoretically, I suppose you could make it as large (north to south) as the widest expanse of the Sahara - somewhat over a thousand miles. Length (East to West) could be another issue.
Also, are the locals colonists? Did some kingdom in the ancient past (or recent past) colonize the continent - only to collapse at some point after, leaving the colonists to develop on their own or die out? Or did the locals develop civilization in this place? If that is true, has the land always been desert, or has something happened that has made it desert? Perhaps some deity associated with rain and storms was slain, resulting in a world wide dissication until a new one can replace the lost deity?
Lastly, what races are present on this continent? All of the standard D&D races or only a few? And where on the continent are they located? Or are they evenly mixed in all areas?
Anyway, please give us more information on the setting so we can help you further flesh it out.
