Partition an External with information still on it...?

Is it possible to partition an external hard drive when there are still files on it? I'm on a 15"MBP OSX10.4 and I'm using a 500gb WD mybook studio edition.

My mac has been running a bit iffy lately and I wanted to back it up but don't have enough money right now for another external. I already have about 300gb on it and wanna try to split it into 350/150.

If it is possible can anyone give me directions or point me to a site where I can figure it out?

Thanks,

It is possible with Disk Utility IF there's enough free contiguous space to create another partition. Since you already have 300 GB on that external, I rather doubt you can do it. What format are you using on the external drive?

If it's formatted as FAT-32 rather than HFS+, you can use the free GParted Linux utility to non-destructively create another partition.

Regards.