Sequence problem in database

Hi,
I create a database in access. For example, There is a table named 'table1'.
There are 3 field in this table,'projectId','taskId','description';
The data type of taskId is sequence.
When i add any data in this table, i want the value of taskId to be increased according to projectID(also project ID is sequence) Is it possible?If so, how?

Thanks!For example:

projectID TaskID
1 1
1 2
2 1
2 2
2 3
1 3
1 4
3 1
2 4

blah..blah..

Thanks!