Huge tables and performance

[Justin Davis]

Hi peoples!
I have an issue with a few big tables that seem to be affecting my system's performance.

I have thought about writing something that will select everything before a certain date, write it all to a table (eg: stock -> stock_archive) and then do a delete on the live table (eek!)

We would like to have 11 months worth of data in our main transactional table, and all relevant data will be cleared monthly.

I'm sorry to say, we don't have a DBA as we are a small company so we have a lack of DB prowess :(
Hence our first solution above :D haha.

Is there any advice you could give me regarding making this happen in MySQL?
Am I even doing the right thing here by trying to make the tables smaller?

Thanks very much!