Auto Incrementing-&>Updating Values In Two Related Tables :Help!!!

hi there,
 i am new to sql server database.i am doing small projects right
now using asp.net and sql to create webpages (very basic webpages)
My problem is:

Problem :
 
   i have two tables .....table 1 and table 2.
                   
                   
                   
    Table 1 has following fields: studentid,student name,student address.
                                                               
Table 2 has following fields:studentid and course .
  table1 student id is the primary key refrencing table 2 student id.
Now i delete a record in table 1 which will in turn also get deleted in
table 2 . so for eg  if i have three records 1 ,2 and 3 ....then i
delete 2 in table 1 ...i will have 1 and 3 in both table 1 and table
2....now i want 3 to become 2 in both table 1 and table 2...so that i
dont have empty space between two student id's 1 and 3. so this is my
problem....if any one can help me out with suggestions please
do.  
                                                                                 
thank you all........
                                                                                                           
     ahmed_ind