Depending where you are based, you may be better going through a BusinessObjects reseller - they also provide training and consultancy to help you get up and running.
One word of warning though - be VERY clear what you want to deliver before you engage anyone in this. That is, understand how many designer and user licences you want for example as well as what reporting functionality you intend to deliver. Some of the guys on here work for resellers and depending on your location would be happy to help out.
It all depends: How many concurrent users are we talking here? Do you need WebIntelligence or also Xcelsius, Crystal Reports, Explorer/Polestar, Voyager/Pioneer, etc., etc.
Otherwise you might want to start with BusinessObjects Edge(not Enterprise) geared towards smaller companies.
See here (including free trial) on how to purchase BOE Edge.
As far as I know BusinessObjects software is not sold in stores (but for Crystal Reports and Xcelsius, which can be purchased online at SAP), so either you go through SAP or through an authorized reseller.