Hi olu,
Firstly, globals are generally a no no in web apps.
But you have lots of methods available to achieve what you want.
You can just call your windows procedure inside your web app and pass it a parameter as you would in a normal windows app eg L:TotalInvoice = CalcInvoice(p_web.gsv('Inv:Number'))
Add the p_web as an optional parameter (so as not to break you windows app) and simply use your p_web variables inside your windows procedure.
Create a new table and read and write data to it based on the session id. You would still need to pass the session id to the win procedure but if you had lots of variables to pass this could be an easier way.
You could use ini and xml files in the same way as the method above.
Hope that helps,
Cheers,
Kevin