[Lee Olivas] “some of my machines have shown signs of hard drive crashing according to my PC I.T. people”
not sure what this means. If these are the original hard drives then they are very long in the tooth and have outlived their expectant life. If they are still working but crashing then it is most likely either ram going bad or system corruption. I would make a clean copy on one machine by wiping the drive clean and reinstalling the OS and all your apps. Do the needed updates and see if is running well. You might also run the original hardware check disc that came with those macs. There are free utilities you can download on-line to check your ram.
That said a new mac mini will run circles around these old macs. Do a search for each piece of software to see if they are compatible. Determine the cost of connecting your monitors to them. Start here: https://support.apple.com/kb/ht3382 then look up adapter prices.
If it really is the HDs they can easily be replaced with larger cheaper faster drives but check with Apple as to compatibility.
Apple only officially supports FCP 7 and FCP X on Lion. Not saying it won’t work — google it. FCP 5 does work on intel Macs but Lion is new.
OSX 10.5.8; MacBookPro4,1 Intel Core 2 Duo 2.5 GHz MacPro4,1 2.66GHz 8 core 12gigs of ram. GPU: Nvidia Geoforce GT120 with Vram 512. OS X 10.6.x; Camcorders: Sony Z7U, Canon HV30/40, Sony vx2000/PD170; FCP 6 certified; write professionally for a variety of media; teach video production in L.A.