It is quite straightforward as both platforms use a common CLI. Now there have been significant changes between 6.3 and 7.0 (FWSM 3.1 is based on PIX 7.0). What I'd do is take the PIX 6.3 config and load it onto a lab unit. Upgrade the lab unit to 7.0. Copy the new config (it will automatically adjust to the new 7.0 CLI). Go the FWSM and rebuild your interfaces manually (FWSM is all about VLANs while PIX/ASA refer to physical interfaces and subinterfaces). Once that's done, you'll be able to copy/paste a large part of the PIX config into the FWSM. Features such as VPN and IPS won't work on FWSM but the rest should be accepted
with no major issues.
