My mac is not let me save on my simpledrive, it lets me take them off file

Yes Mac and Windows use 2 different and incompatible hard drive formats. However, there are many files that can be opened between the two. Mostly media and some docs. Try uploading to somewhere like MS Windows Live Skydrive or simply email. Then download. This is a quick fix. I heard you could use file sharing, but that requires a network. Even burning to a disc should work.

The external hard disk must be formated in a file system that both the pc and the mac can use - best is FAT32. In your case the file system that the mac put on the disk is incompatible with the pc.
Make sure the files you want to move are still on the mac (if not copy them back from the disk), plug the disk in the pc and format it there in FAT32 (don't use the quick option), plug it in the mac and copy the files and unmount the disk before disconnecting it from the USB connector. Now you can put it in the pc - in there always use the Safely disconnect icon, don't just yank out the cable.

Your Mac can't recognize the 320 because it's formatted as NTFS and Mac uses Mac OS Extended (Journaled) format. You need to install one or two apps on the Mac; Crossover or Parallels, and then install the Windows software on the Mac you need to read and use the files.

At that point, some files which share file types in Windows and Mac could be transfered (jpeg, mp3-4, etc.)

You'll learn maybe more than you wanted to,

Good Luck,

Marcus

Were you using this on a PC? it may be using Fat or NTFS. If it's seeing the drive and you can't use it, it may be the filing system, I believe macs use a different one than PC's. I would copy the files "if possible" to another flash drive or computer and just re format the 320 gig drive, the mac will install the right filing system for the drive and it should be good to go.

Your device has been formatted to the PC format and the MAC doesn't recognize the extension.
From the Simple Tech site (troubleshooting):
If I wanted to use the portable drive on a MAC "and" a PC, what is needed? For use on a MAC and PC you will need to re-format the drive to be compatible. You can do this by going to disk utilities and selecting "the drive" (not the untitled volume). You will then select "erase" from the top of the screen. The process will allow you to select a format option. You should choose "MS-DOS File System". Then select the "erase" from the bottom of the screen.
Once the process is complete, you will have an additional folder on your desktop that is the SimpleDrive. You can copy and paste or drag and drop file to it. If during the first pass you are unable to change the volume format option, please repeat all steps and it should allow you to select this on the second try.

Copy all the data onto your Mac computer.

Take the external drive to a PC computer, and "reformat" it, using "quick format".

Take the external drive back your Mac computer,
and write all the "saved" files onto the drive.

they may be "read only" right click on one of the docs (assuming they are Word files) go to properties - untick the box that says read only.

when you saving files - go to save as 97 to 2003 doc

the global template (normal.doc) may be saving as read only

Here are some recovery programs you may rely on. Both programs can recover photos, videos and music.

Photo Music Recovery Software (for Windows)
Mac Photo Music Recovery Software (for Mac OS X)

A Tip: Before your items are recovered, do not attempt to save more files the original files(your photos, music) are overwritten.

Most of the times you just have to format the drive to Mac OS Journaled or else you will only be able to transfer 4gb or less at a time.

This is a format problem, unfortunatley the mac has a different file system than a regular PC has. A mac can write PC files and mac files. PC's typically are not vice versa in writing to a mac hard disk. Only way around this one is to format the drive to be a PC drive. Then the mac and the PC should see it.