Cannot copy files over?

WD External Drives External Drives for Mac
5

I am currently using both Windows XP and Mac OS X. My drive is WD My Passport Essential SE 1TB. Current format NTFS. 

I would like to be able to keep using the drive on both OS’s for storage. How can I do this?

PS: I can already read from the drive using either OS however only Win XP is able to write on the drive–which i would like to remedy.

Please help.

Thanks in advance!