One is made by Oracle and the other by Microsoft.
Well it is almost like comparing Apples to Oranges, there are many differences.
Major ones I know. In SQL Server a Stored Procedure can return a cursor directly, in Oracle you need to do some hoop jumping, not much mind you, and not one that I would say the because SQL Server handles it easier that SQL Server is better. It is not.
Oracle allows you to better control how your database runs. It allows you to get more under the covers and tweek environments to best fit your needs. SQL Server hides most of this, to "Dumb" it down.
Oracle is cross-platform, SQL Server is not, it only runs on Windows, and will need special tools to have UNIX systems access the Data.
Now those are just a couple, and my opinions. Do not take them as gospel. I am very knowledgable, but far from being an expert. I am also pretty anti-Microsoft. Even though I program in 4 of Microsoft's languages. Foxpro, VFP, VB 6.0 and VB.net.
Oh, one other major difference. Price. Oracle is much more expensive, and probably requires much heftier machines to run it, with many hard drives mirrored, and data files spread evenly over the hard drives to minimize IO.
Good Luck
Mark