External drive not mounting

Hi.

I am using a macbook pro with 10.5.8, and have an external hd (freecom 320gb). I have used it for around a year and it is almost full. The other day, after attaching it to a pc - when i now attach it to the mac, it does not mount, and the warning 'this disk is not recognised' etc comes up. It shows in disk utility, but does not allow me to verify/mount it. I'm guessing the pc has reformatted it or something

What can I do?! I have looked into data rescue software, but I'm not sure - the information cannot just disappear? and I just want the drive to have the same architecture, as all my music etc was organised in particular folders.

Thankyou

Does the PC recognize it? I'm sure you would know if it had been re-formatted, as Windows would have asked you first.

the pc recognises it yes... but when i connect it to the pc, it asks if i want to reformat it - obviously i click 'no'. then if i click on properties, it shows the drive as being full (0 bytes available).

plus...

in 'partition type' it says "Windows_FAT_32"

is this relevant (i'm guessing it is). i have another identical drive which is working fine (slightly larger, 400gb), and with this one, in disk utility, instead of "partition type", it says "format", and then "MS-DOS (FAT32)"

thats the only difference when looking at disk utility.