Most of Canada, including Softrak, has been on holiday the past two days, so you will probably hear from them tomorrow, but here is my two cents worth..
Yes, Adagio Payables (as well as Adagio Receivables and Invoices) integrates with ACCPAC Plus Job Costing. Yes, you need the ACCPAC Plus Windowing System Manager to run any ACCPAC Plus module, including ACCPAC Plus Job Costing.
No, Advantage Series Job Costing doesn't work at all with Adagio. You have to think of Advantage Series as a completely different program from ACCPAC Plus and Adagio - the ONLY integration it has is that its GL can retrieve ACCPAC Plus/Adagio subledger activity.
However, I believe the real answer to your question is to wait a few more weeks for the release of Adagio JobCosting. I don't know anything definite, except that I have seen the new Softrak Dealer Price List effective Jan 1, 2005, and it is listed as an available module. I have been using the beta version in house for a few months, and it is worth waiting for.
Steve Schwartz