Date Creation In SQL

Hi,
I have a parameter that is being input as a String via Crystal Reports.
It's called 'School Year'
and a typical value is '2006'. I need to be able to create a 'Date'
that is compared to a field value in a where clause. In this case the
db field is called 'requisition_time_stamp' in the T_ORDER table. The
'requistion_time_stamp' file is of type 'datetime'.

Below is pseudo_code for what I need to do:

T_ORDER.requisition_time_stamp >= Date(ToNumber(School Year),6,1)
AND
T_ORDER.requisition_time_stamp < Date(ToNumber(School Year + 1) , 6,
1)

The 'Date' method is a mock-up and is problematic because the 'School
Year' field needs to be converted to a number so it can be incremented
in the second statement, so I also need a conversion method, something
like 'ToNumber(School Year)' .

I've looked at the Date functions in the Sybase documentation and I
don't see anything that fits what I'm trying to do.

Any help would be greatly appreciated!