You sir, have what is often referred to as a conundrum.
Your G5 cannot and will not boot OS9 directly. It
will run OS9 Classic - a stopgap mostly-functional OS9 that helped bridge the divide between OS9 and OSX. You need to install OSX 10.4 "Tiger" which will allow installation and operation of OS9 Classic in a sort of "sandbox" inside OSX.
Here's the conundrum: That capture card
may or may not work under Classic. Because Classic runs "inside" OSX, it does not normally get direct access to I/O like Firewire ports. There are many, many folks who keep older Macs that
do natively boot OS9 or earlier to run things like older drum scanners, lithographs etc. and similar stuff that was never ported to OSX. Heck, there are even a few dummies around here that use it to produce music…
It's a crapshoot with no better than even money odds that you can make your G5 happen here. You can only load up, spit into the wind and try.
Download the dmg of the retail Tiger DVD here:
https://www.macintoshrepository.org/12343-mac-os-x-10-4-tiger-for-ppcInstall it.
If OS9 is not included in that, grab a Universal drag and drop here:
http://macos9lives.com/smforum/index.php/topic,1859.0.htmYou'll then have to see how well Final Cut will run under Classic, if it runs at all. THEN you can try to access the capture card and import something.
If it works, thank your lucky angels. If not, your best… Hell, your ONLY real solution will be to grab the fastest G4 you can find like a 2x1.25 GHz or 2x1.42 GHz Mirror Drive Door model that immediately preceded the G5. Anything older (and slower) than that will have you watching your lawn grow waiting for stuff to render, transcode or whatever.
Good luck.