The easiest way in MS SQL 2005 and up is to use the SQL Management Studio, go to Views, highlight the name of the view you are interested in, right click, select Script View as/Create to/Clipboard.
open up notepad or your prefered editor and paste the contents of your clipboard. The SQL used to create the view should show up in your editor.
If this doesn't work, or if you are working with older versions of SQL Server, look at the system objects as follows:
use [YouDatabseInstanceName]
go
select * from sys.objects
where type = 'V'
and name = 'YourViewName'
-- capture the object id and schema_id to examine later
-- object_id = 436921992
-- schema_id = 1
-- this should show you whether or not there is anything set in the definition coloumn
select * from sys.sql_modules
where object_id = 436921992
-- use to examine which schema name the view is in
select * from sys.schemas
where schema_id = 1
-- Use this to capture all the views by the schema name
select o.name
,o.object_id
into #views
from sys.objects o
join sys.schemas s
on s.schema_id = o.schema_id
where o.type in ('V')
and s.name = 'dbo'
select * from #views
-- use this to examine the definition of all views
select definition + char(10) + 'go' + char(10)
from sys.sql_modules c
join sys.objects o
on c.object_id = o.object_id
join #views o2
on o.object_id = o2.object_id