Thanks for the response Lars, I will look into ntile and window functions.
As to your last point, I guess I should have spent some more time in better formulating my question because I inadvertently gave the impression of not having searched first, which is certainly not the case. However most of the solutions that I encountered involved nested queries and self joins which I want to avoid as the query is for a fairly large table. I posted the question here because basically I wanted to know if a select top x percent query was possible.