We've got an older windows xp machine with an intel server motherboard + xeons, and I was thinking of converting it into a raid file server / backup setup. Any suggestions would be greatly appreciated, as I'm not sure how we can make it reliable + have it accessible by both the macs and pc's in our office.
Right now I'm thinking of adding a sata to ide raid card with a couple of ports, mounting a couple of large hard drives and putting in a gigabit ethernet card. That's really all I'm thinking right now, so help me out!
I would suggest FreeNAS here is the link. I have it running on a P2 box and I can access it with XP, Macs and Linux. It isn't the fastest solution out there but it would be plenty quick on your hardware (since it's not 10 yrs old like mine). It's also small and free so it's easy to try and if you don't like it just try something else. I like it so I never bothered switching.
It supports software and hardware RAID cards and is fairly easy to set up if you have messed around with other NAS's (web interface is much easier than linux, though not as robust). I also use it for rsync backups every night and it has been stable (currently up since our last power outage 87 days ago). It doesn't have robust multi-user functions which might not work too well for what you want, but I love it for easy LAN file serving and backups.