DUDE, GET RID OF THE MAXTOR AS SOON AS POSSIBLE. Maxtor drives are well known for their fuck-ups. I had a Maxtor 160gb 10k RPM SATA drive in my PC that I used only for the OS and to store renders/mixdowns/bounces. It fucking died on me a week or so ago with the error "UNMOUNTABLE_BOOT_VOLUME", the fix was to put it in another PC as a slave, and when Windows boots up it runs Chkdsk on it. I put it back in my case, the PC booted up like normal, and I started backing up stuff to DVD-R. I left the house, came back, and it had frozen like 20 minutes after I left. The PC will NOT boot up anymore now. The drive is gone, it's just fucking gone! Non-repairable. My girlfriend's mom is dating this guy from Dell, he's what you call an "anti" employee, which means he works for a place and promotes it, etc., but he'll tell you every little secret you're not suppose to know, especially the loop holes for customers. He's a tech guy, a real nerd, and he said once a drive does that once, it'll only work that one more time, giving you enough time to backup anything you want. Then it's all gone.
On a sidenote, I had ordered a really nice WesternDigital drive, same storage and RPMs...but Dell threw that POS Maxtor in there. My advice, make sure to backup everything on that drive that you don't want to lose and get a different brand (Seagate/Glyph, Western Digital), it just might happen to you too.
Moving on...as far as the question you posted, I have an external 250GB FireWire400 drive that I use for tracking and it has my DFHS stuff on it. I have had ProTools sessions from my PC on it, and then I've plugged it into my Mac, and the Mac read it fine. Even wrote to it! I could copy files, put new files on there...it was neat. But when I had it formatted for my Mac, and tried to do that with the PC...it wouldn't even recognize the drive was connected. Using all 4 FW400 ports, and trying all 8 of my USB ports. Then I wiped the drive using my Mac, and plugged it into my PC, and it saw it, then I could format it for Windows (NTFS) again.
Macs are friendlier than PC's, they share n stuff. Thats what I learned from that.
~006