yeah i have this external hardrive running under mac os extended (journaled) and i was wondering what formatt works under both mac and windows and if so how to comvert it without loosing files
You can't covert formats without re-formatting, which destroys all data on the drive. Your only choice is to back the data up to somewhere else and reformat the drive.
There's a software. iPartition - http://www.versiontracker.com/dyn/moreinfo/macosx/23828 - can do just that. However: It's not free, and I'm not aware of a free alternative that's able to do that. A cheaper alternative would be to get a friend or shop to lend you a drive for transitioning, i.e. you copy all your stuff to an additional drive, reformat yours, put the stuff back, erase your stuff from the interim drive and give it back with a good bottle of wine or something.