Hi
We do very similar things with SAP and Siebel CRM. Our web properties are in PHP and Java, but our ERP properties is in VB or ActiveX. We have PHP running from a Windows2000 box. PHP from windows has the unique capability of connecting to COM objects, so we use the inbuilt or written activeX objects, pass parameters, obtain values, store them in a Oracle 8.15 DB, plot gd based graphs. We have schedular kicked out to obtain stats for load balancing.
Read the article in phpbuilder for COM objects, a good one for the starters.
good luck !