MySQL server version 5.0 have some spatial capabilities. It can create and store geometry objects, as well as fetch them and check their relations using Minimal Bounding Rectangles (MBRs). Untill now it lacks advanced functions like Distance(), ClosestPoint() and other important features.
On the other hand new relise of MS-SQL Server 2008 have many usefull spatial functions. Look at following blog resources:
Isaac Kunen. MSDN Spatial blog
Dave does Data. David Lean MSDN blog

	Some spatial data about Milan city	2008-02-23
	Create points using SQLserver Spatial	2008-12-16
	Create polylines using SQLserver Spatial	2008-12-16
	View number of spatial layers using UNION ALL (SQLserver Spatial)	2008-12-17
	MS-SQL 2008. Query spatial data [1]	2009-02-17
	MS-SQL 2008. Procedure to find N nearest neighbors	2009-02-25
	MS-SQL 2008. Extract vertices from polyline in spatial query	2009-03-04
	MS-SQL 2008. UDF function that constucts geographic point	2009-03-10
	MySQL. Create and populate spatial table	2008-06-09
	MySQL. Create polygon geometries	2008-06-09
	MySQL. Function to measure distance between points in Lat Long	2008-06-12
	MySQL. Check relations between geometries	2008-06-17