RE: GP Web Client add a button to specific form
First, let's deal with the button.
To add a button, you will need Modifier.
1) Open the window you want to add the button to
2) Go to the Tools menu on the window, and choose Customize > Modify Current Window
3) In Modifier, add the button where you need it to display. If you add it to the control area, it will show on the ribbon
4) Save the modification and return to Dynamics GP
5) Go to Administration > System > Alternate/Modified Forms and Reports. Choose the DEFAULTUSER role, then from thte Product DDL choose Microsoft Dynamics GP, from the Type DDL choose Windows. Depending on the window, expand the series it belongs to and locate it, change the radio button to the modified version
6) Click save.
This button should now show up in web client.
As for the customization portion, you will need to either write it in Visual Studio or use GP Power Tools to write it. If you choose the Visual Studio route, you will need to DAG the modified forms dictionary and reference it in a Dynamics GP project in Visual Studio (this assumes you already have installed Visual Studio Tools for Microsoft Dynamics GP).
If you choose the GP Power Tools route, well, I am assuming you have GPPT to begin with. Launching a URL is the simplest thing to do. You can use the Visual Studio Tools helper library or you can use a bit of Dex code in GPPT to get the job done.