T-SQL 2005: Add Date and Time

I have two fields which are both Datetime type:

Date = '2011-1-01 00:00:00.000'
Time = '1900-01-01 3:31:19.000'

The '1900-01-01' is the default value so I am interested only in the time part (3:31:19.000).

All what I want is to combine Date and time together. So, for this example i want a query which would give me the result:

Combined = '2011-1-01 3:31:19.000'

I am using T-SQL 2005.