Yep... it's call a "Cross-Tab" or "Pivot"... and the type of table you have is called an "NVP" or "Name/Value Pair" table...
SELECT ID,
MAX(CASE WHEN Field = 'UserName' THEN Value END) AS UserName,
MAX(CASE WHEN Field = 'FirstName' THEN Value END) AS FirstName
FROM dbo.yourtable
WHERE ID = @ID --Remove if you want to do the whole table
GROUP BY ID
For more information on this subject, please refer to the following articles...
http://qa.sqlservercentral.com/articles/T-SQL/63681/
http://qa.sqlservercentral.com/articles/cross+tab/65048/