Table is growing too big

I have a table that receives data every second.  What I need to do is limit the size of the table so it stops growing ( I cannot change the time for input ). We do not need to keep this many records and I have decided on the time frame to keep. What I would like to do is create a trigger that after INSERT, DELETES the oldest row, I assume this will keep the table at the size I want. Any suggestions for code? Will the INSERT and DELETE trigger slow down the DB because its every second? Or is there another way to accomplish this with as little impact as possible. I just need a starting point!