I think starting SW2008 SP3, one needs to be on subscription to install the service pack. If you were on subscription hen SP 5 was released then please contact your VAR to help you with the installation.
Copy the "my documents/solidworks downloads" folder from your old machine. That should have all the files to update from sp0 to sp5. Best way is to. Do a "download only" for the sp that's current, just before your maintenance expires. Downloading software is a service that is included in the subscription contract.