I think I’ve heard of people running Final Cut and Avid on the same system…search the archives here, I’m pretty sure I’ve read about it here in the past.
Also, I’d suggest getting a 2nd internal SATA drive. Like, 250 or 300 GB. I use my primary drive for Applications, iTunes, and iPhoto storage (they default to the system drive), my external drive for captured video, and my second internal drive for everything else. From graphics, to spreadsheets, to my web page, to DVD projects and finished DVD images. I find I often want to keep thigns (like DVD projets) for quite a while after I’m done with them, so I let the drive get up to about 90% full before I start erasing old stuff. I’m afraid that if I let my system drive get that full then my applications would start to get sluggish, so I keep the second drive for files. I just feel better when my system drive is more than 50% empty. That’s just my opinion, but I thought I’d suggest it.
As for starting “fresh,” start out by printing this document:
https://manuals.info.apple.com/en/Installing_Your_Final_Cut_Pro_Software.pdf
Hold on to that for now, I’ll get back to it later.
Once you’re ready to erase, put your OS X CD or DVD into the machine and restart holding the “C” key. Once the CD loads, find the Disc Utility in the pull down menus and erase your drive using the “Zero all Data” option and make it an “Extended” format. You can leave Journaling off or on. I think some say off, but I don’t think I’ve heard of a problem with it on the system drive. (Do turn it off for any media drives when you format them, however.) Then install OS X.
After you reformat and re-install OS X the FIRST thing you should do is to get it online. Run the software update and re-start. Run it again until it tells you there is nothing left.
Then get that PDF I gave you earlier and follow whatever it says.
After that, run software update again, and then to to Applications/Utlities/Disc Utility and repair the permissions on your system drive.
Then install any other software you have, run software update one more time, and restart with the OS X CD and hold “C.” Once that comes up, open disc utility and repair permissions one last time. Then restart without running the installation program and you’re good to go!