Partitioning a table vs moving entries to another table
Partitioning is helpful with large tables and management purposes for your DBA.  If you have 50GB of data you should start looking into partitioning just for perfomrance alone, as Kim Tripp stated.  

However, as a DBA I find partitioning great for management of large tables and reporting data that comes from a OLTP source, something which I think you are describing.  Partitioning will allow you to also create different indexes, different fill factors, and utilize indexed views on top of them to gather massive performance boosts for aggregation type functions utilizng "Indexed Views over Partitioned Tables".

In my recommendation, get familiar with partitioning.  It can save you disasters.  I once inhereted a table that was 6 billion rows and growing at 2-3GB a day with only 20GB free on the drive.  I was able to create a new partition for new data, copy out all the old data to different databases on RAID 5, and update the code to refer to views; all without client downtime in a 24/7 shop.  Partitioning is essential as data sets grow larger.