You can add additional list of the payment gateway from the config wizard by doing the ff:
From wizard.aspx add:
Code:
<<asp:ListItem Value="YourCustomGateway">Your Customer Gateway</asp:ListItem>
From wizard.aspx.cs, open the {root}/admin/wizard.aspx file, find BuildGatewayList() method, and add:
Code:
gateWaysPerFeature.Add(new ListItem("YourCustomGateway"));
As for the "Access to the path 'C:\comtest\Web\checkoutreview.aspx.vb' is denied." error you're getting, could you right click on that and make sure it's not a read-only file?