I'd like to filter a sharepoint list view of tasks to only show items
for the "current payroll cycle", which is a calculation based on the
current week (Friday 5PM + 7 days).

Currently I can sort of do this with custom columns on the view that do
calcuations on current date, but this requires each task be updated each
day since [Today] isn't officially supported (I'm using the "create a
Today column and then delete it" hack). I also have to keep a bunch of
columns that contain bits of the calculation to determine the current
payroll cycle (julian days etc).

It seems to me a incredible shortcoming of sharepoint if I can't do
advanced filtering on a list based on current day. Can I create a filter
in sharepoint desinger that could do this? I basically just want a SQL
query kind of like this....

select taskname, duedate, priority, complete% from sharepoint_task_list
where duedate BETWEEN *calculation of friday before sysdate* AND
*calculation of friday before sysdate + 7*

Is this possible in designer? I've heard there's a query language called
CAML for sharepoint, but does that require custom code to use?