area constraints

hi, 
 I have some elementary doubts regarding flooplanning .. 
hoping a quick guidance here ..(not a hw)  
In xilinx floorplanner or manualy (using ise 5.1) 
1. Can i assign flexible area constraints to individual modules in a design.. 
i mean, can i say a module shud fit in this much area of some shape .. 
without specifying absolute slice locations in area group ? .. and 
2. can structures other than rectangle be specified ? 
i guess i am missing something obvious :( ?
thanks a lot,
ay