you only get grainy shadows with raytraced shadows. so if you would use those shadows without changing the settings you would get sharp shadows.default raytracedshadows are sharp.the default deepth mapped shadows are blury but not grainy. so you dont talk about those.

if you are talking about DM shadows then you need to adjust your shadow-cam. there is a tutorial on this forum and smithmicro.or use a higher resolution for shadows