help on find data

dear all
i have that call xyz that has data taken from a field machine
this table has data structure like this
================================================== ====================
= QUEUE (type nvarchar) === TIME ( type nvarchar) == DATA ( type
nvarchar) ====
================================================== ====================
= x1 ==== 2008-03-07 12:17:50.274 ==
23.0034 ==
= x1 ==== 2008-03-07 16:17:50.274 ==
28.0034 ==


i need to create a query that will ask me to select the variable ( which is
x1 ) the the intervale of data and time ( for ex. from 2008-03-07 to
2008-03-07 for day and time of houre is between hour 12:00 to 20:00 and give
the the value
how can i do this in sql knowing that are field are nvarchar type
your's
wael