I'm not really sure if there is a specific Freespace 1 forum, though you may find some help here.
As for Freespace Open, that does indeed require Freespace 2 to be installed since it's built on the FS2 source code. The team ported the FS1 campaign to FSO under the name Freespace Port. It's technically a different game, but isn't noticeably different (without using the upgraded graphics), and with the upgraded graphics you can get through FSO, it's not necessarily a bad choice.
As for FS1 itself, what sort of system are you running, and is FS1 running in any sort of compatibility mode?