They will produce exactly the same results, yes. My comments would be that you should avoid the NOLOCK hint, adopt a clear layout style to help people understand your code, qualify names correctly, use aliases, and pay attention to casing ('username' versus 'UserName'):

SELECT

U.*

FROM dbo.Users AS U

JOIN

(

SELECT

U2.UserName,

MAX(U2.GWP) AS MGWP

FROM dbo.Users AS U2

GROUP BY

U2.UserName

) AS A ON

A.UserName = U.UserName

AND A.MGWP = U.GWP

If you're interested in why both query forms produce the execution plans they do, I wrote about that here:

http://sqlblog.com/blogs/paul_white/archive/2010/07/28/the-segment-top-query-optimisation.aspx