DLookup Equivalent In SQL Server

I am migrating a student database from Access to SQL Server. In Access
I have a query that displays grade information (grades are calculated
on a 12-point scale). In the query I average the students' scores and
store it in a column called Avg. I look up and display the equivalent
grade letter using Access' DLookup function from a table called
GradeTable_tbl. Here is how it's built in Access:
Grade: DLookUp("[grade_letter]","GradeTable_tbl","[grade_num]= " &
Int([Avg]))

Here is the structure of the GradeTable_tbl:


grade_num grade_letter
0 F
1 F
2 D-
3 D
..
..
..
10 B+
11 A-
12 A


How would I do the same thing in SQL Server? I want my output to be
something like:


Student Score1 Score2 Score3 Avg Grade
Bob 12 10 8 10 B+
Nancy 12 11 11 11 A-
etc...


I appreciate your feedback!

-Paul
------
"You never know enough to know you don't know"