You have two options I know of to 'de-Orange' the San Francisco. You can use something like Titanium Backup (requires root) to remove the Orange apps, or install a custom ROM.
On my San Francisco I rooted the phone (see first part of this video or you could use Super One Click) and then used Titanium Backup to uninstall the Orange apps (list in this thread). If in doubt, TB lets you 'freeze' apps so you can make sure everything still works before uninstalling fully.
Alternatively, you can install a custom ROM (see full video) which I haven't done yet (waiting to see if FroYo ROM becomes available).