Hi John
Try the following command
"write memory" or "wr mem" for short.
Attached is a link to the configuration documents for pix firewall software versions.
http://www.cisco.com/en/US/products/sw/secursw/ps2120/products_installation_and_configuration_guides_list.html
You can upgrade to 7.0 depending on the type of pix you have.
Pix 501, 506 cannot be upgraded.
Pix 515E can be upgraded but you may need to upgrade the memory first (Needs 128Mb of memory for v7.0)
Pix 525 & 535 can run version 7.0 and don't need a memory upgrade.
HTH
Jon