Steve already couvered the DRP part.
Just to add a little bit to Keep in mind:
- SQL2005 has many features "off by default" on a fresh install. If you perform an in place upgrade from an earlier version, the installation process will activate the needed options, to be sure everything will keep on working.
- SQL2005 is more strict (granular) on os-level authorisation.
- If you have (scheduled) dts packages, be sure you know what an upgrade does to your packages !
( install downward compatibility packages for dts, in case it cannot translate all to SSIS, because it wil "port" the dts package as an object on itself)
- Don't choose an in place upgrade, because that seems to be the easy way !
- as already stated, you should start with "sql2005 upgrade advisor". This tool will point you to potential issues on many levels.