Payment Gateway Setup (SagePay)

Overview
Please follow the instructions below to activate this gateway. If the payment gateway's interface has changed or if the screenshots (where applicable) look different, please let me know.
SagePay - Setup
1: Sign up for a SagePay account to receive your vendor name and encryption password.
2: Enter applicable details in your Maian Cart admin area:

Sales > Payment Methods > SagePay
SagePay - Callback Url
The callback url for all operations is:

http://www.example.com/checkout/sagepay.php
https://www.example.com/checkout/sagepay.php (SSL)

Where 'example.com' is your own domain.
SagePay - Sandbox/Simulator
SagePay has 2 test options, a simulator and a sandbox system. Note that for each, a different test url is required (see docs).

It is recommended a test is run with the simulator first, before the sandbox. You`ll need to contact SagePay for a sandbox account if you don`t already have one.

Simulator:
https://test.sagepay.com/simulator/

Sandbox
https://test.sagepay.com/mysagepay/login.msp

Test cards for sandbox account:

Visa: 4929000000006
Visa Delta (Debit): 4462000000000003
Visa Electron UK Debit: 4917300000000008
Mastercard: 5404000000000001
UK Maestro: 5641820000000005
International Maestro: 300000000000000004
American Express: 374200000000004
Japan Credit Bureau (JCB): 3569990000000009
Diners Club: 36000000000008
Laser Cards: 6304990000000000044

Security:

CV2: 123
Billing Address: 88
Billing PostCode: 412
3D Secure password: password