See this link for sagepay's take on it
http://www.sagepay.com/products_services/bolt_ons/pci_dss/which_level
and
http://www.sagepay.com/products_services/sage_pay_go/integration/inframe
Note this is a UK gateway dealing with UK merchants. In the UK PCI compliance and in particular PA-DSS has not got the same deadline as in the USA. The UK is about 3 years behind. For example the absolute deadline for PCI compliance is September 2010 and PA-DSS certified applications has not been meantioned....