Products are a custom entity now... I have tried to get it to work for you but I always get an error on saving the product, maybe someone will be able to help; I have tried 2 ways, using data bindings and without...

 No data bindings:

'create the opp
        Dim opp As Act.Framework.Opportunities.Opportunity = ActApp.ActFramework.Opportunities.CreateOpportunity()
        opp.UpdateContacts(New Guid() {ActApp.ApplicationState.CurrentContact.ID}, Nothing)
        opp.Name = "test"
        opp.Update()

        'create the product
        Dim product As Act.Framework.Opportunities.OpportunityProduct = _
        ActApp.ActFramework.Products.OpportunityProductManager.CreateCustomEntity
        product.SetOpportunities(ActApp.ActFramework.Opportunities.GetOpportunityAsOpportunityList(opp))

        'set a name
        product.Name = "test"

        'save the product
        product.Update() '<<<<-----error saving here

Data bindings:

'create the opp
        Dim opp As Act.Framework.Opportunities.Opportunity = ActApp.ActFramework.Opportunities.CreateOpportunity()
        opp.UpdateContacts(New Guid() {ActApp.ApplicationState.CurrentContact.ID}, Nothing)
        opp.Name = "test"
        opp.Update()

        'get the current product list for the opp
        Dim plist As Act.Framework.CustomEntities.CustomEntityList(Of Act.Framework.Opportunities.OpportunityProduct) = _
        opp.GetProducts(Nothing)

        'add the fields
        For Each field As Act.Framework.ComponentModel.DBFieldDescriptor In ActApp.ActFramework.Products.OpportunityProductManager.GetFieldDescriptors()
            plist.FieldDescriptors.Add(field)
        Next

        'create a binding source and bind to the product list
        Dim bindingsource As New BindingSource
        bindingsource.DataSource = plist

        'create the product
        Dim product As Act.Framework.Opportunities.OpportunityProduct = _
        bindingsource.AddNew()
        product.SetOpportunities(ActApp.ActFramework.Opportunities.GetOpportunityAsOpportunityList(opp))

        'set the contacts, companies and groups
        Try
            product.SetCompanies(opp.GetCompanies(Nothing))
        Catch ex As Exception
        End Try

        Try
            product.SetGroups(opp.GetGroups(Nothing))
        Catch ex As Exception
        End Try

        Try
            product.SetContacts(opp.GetContacts(Nothing))
        Catch ex As Exception
        End Try
        product.Name = "test"

        'save the product
        product.Update() '<<<--- error svaing product here