Not too be picky but if your requirement of the other columns is not needed than what you ask can be accomplished really easy..

SELECT ServerName FROM InstanceTypes GROUP BY ServerName

I'm sorry but I really feel strongly on this point, especially in an IT world such as ours where there are a thousand different ways to accomplish a task. The simplest solution is always the best one.

EDIT

After re-reading your post. Im now thinking you wanted to remove duplicates in the tsql resultset you posted, in which case, only choosing the first row of your ROW_NUMBER column is the best and easiest solution.... Sorry for reading too much into what you were looking for....:)