You don't need a loop, just an If statement. Something like this:
If (cdbl({?Report Month}) = 12) then
{command.oppo_TargetClose} >= Cdate(2009, 1, 1)
else
{command.oppo_TargetClose} >= Cdate(2008, cdbl({?Report Month}) + 1, 01)
There are some other things you can do to dynamically set the year if you don't want to hard-code this report for this year. It would look something like this:
if ({?Report Month}) = 12 then
{Command.oppo_TargetClose} >= CDate(year(CurrentDate) + 1, 1, 1)
else
{Command.oppo_TargetClose} >= CDate(year(CurrentDate), cdbl({?Report Month}) , 1)
-Dell