I've recently bought a new iMac running Lion, and whenever I use my External Harddrive with it I can read from it fine i just can't write to it. However from my Windows PC I could.

According to google it seems my problem is the harddrives formatting type. Everything i've found so far has just been people saying reformat the harddrive and start again. Only problem is i can't lose the data that's on there and there isnt enough space on my PC to copy it off to store it whilst i re-format.

Is there any other solution apart from reformatting and losing all the data on it? It's currently NTFS format