So I had a PC and recently got a MAC. I can still see and view all the files on the external hard drive (its a WD Element, if this makes any difference). But I want to be able to add and move the files around. Is it possible to format the hard drive so that I can do this without erasing all the files on it?

As far as I know...formating a WD Hard Drive DOES erase all the files on it (well I suppose someone like the FBI or CIA might be able to read it but you can't afford that technology.) Formatting has wiped every HD I've ever played with.

I've never used MACs so I can't answer the 2nd part of your question. I hope someone knows the answer.

Jon

You don't need to format the hard drive - you just need to change the permissions. Don't remember how to do this on a mac though. But def don't format it or you'll lose everything.

Formatting a hard drive WILL wipe it, that's kind of the point.

I don't have a mac, but I think macs might prefer FAT32 rather than NTFS? With windows, hdds are often formatted as NTFS, which may be your problem. If so, then the only solution is to format it, in which case you'll need to transfer your files off to somewhere else.

If it's just a permissions thing, then you won't have to. Your best bet would be to google it, you're sure to find something there.

^No no no. LOL, FAT32 hasn't been the default file system for any OS in YEEEEARS. Windows default is NTFS (that's probably what your external HD is using), and Mac's default is HFS+. I swear I thought Macs could write to NTFS drives now, but it looks like I was wrong. You don't need to format the external drive though. Try this ntfsmounter.com

If that doesn't work, let me know. Can't believe mac doesn't include native NTFS drivers. Stupid apple.

Mac computers (Lion OSX) cannot natively write to NTFS file systems; however they can read from them. To write to NTFS, you need to install an additional piece of software (panic suggested one of the many versions available). For Lion OSX we had to buy the software, because the freeware was not working properly.
If you are not willing to try/buy the software, but still want to use your external drive, you need to:
1) copy the files from your external HDD to your computer hard drive;
2) format the external hard drive in HFS+;
3) move back the files to the external drive.
I am not sure, but I believe that Windows cannot deal with HFS+ very well, so to go back and forth between the two OS, you may need to format in FAT32, but then you have an upper limit of 4 GB.