SQL Server 2000 UDF's : Custom Aggregate and Cumulative Functions
If the topic intrigues you, please check out my latest article:
http://weblogs.sqlteam.com/jeffs/articles/1490.aspx
A little too long for a blog unfortunately. Before reading the article, keep in mind it's purely an academic exercise. But the ideas presented are hopefully somewhat original, and might even have some practical applications, who knows?
Enjoy!