Seems like a broad question there bud. Well, what are you looking to do with them? What kind of system will be hosting the database? Is cost a consideration? I like MS SQL 2000 a lot, but it can be quite expensive to license depending on the application and the hosting server configuration.

Oh i'm just asking about functionality of both, not about cost or anything.

Oh, in that case I can say that MS SQL 2000 works rather well. There is a great deal of functionality to it that I haven't touched, but from what I use it has worked very well.
 
Here is a comparison of Enterprise and Standard editions from MS:
 
http://www.microsoft.com/sql/howtobuy/choosing/default.asp
 
also, the Enterprise edition comes with SQL Server Desktop Edition as well. I do like the tools that it comes with (Query Analyzer, and the Enterprise Manager) to manage the servers their respective components. It also interfaces with Office 2000/XP really well, along with Visual Studio/VS.NET.
 
As for MySQL, I only installed it once and never really messed with it, but it seems to be very functional and scalable (this site is running on it right now) and it's free. Maybe someone else can shed some light on this.