In general terms, it should not be an issue. I work on Mac Projects all of the time on my PC.
Now, two things to think of:
1.) unless this has changed, the Mac will only see a FAT-32 formatted HDD, not an NTSF. This limits you on file size to ~ 4.GB. With a program like Mac Drive (might not even be needed with most newer PC's), the PC can handle a Mac formatted external.
2.) I have no issue using .MOV's with the Animation CODEC on my PC. I'd probably convert all AVI's to that, to work on the Mac (boy, I hate typing that blasphemy, but I'll get over it). If I understand correctly, CS4.1 with the latest QT (Pro?), will now handle the ProRez Apple COCEC's. There is a recent thread that makes mention of this.
After you do the setup, you should be good to go. Now, I have only gone one way - Mac to PC, so I could well be missing something.