Attached Link: http://blog.taragana.com/index.php/archive/10-best-open-source-erp-software/

> Quote - ... would like something already written for the purpose of keeping track of inventory and sales.

Quite a few free / shareware / open source programs out there.
Without knowing the sales / inventory volume you're needing to cope with it's hard to be sure I'm pointing you to suitable candidates.