Media bay hard drive problem G3 Wallstreet

Hi,

I have a G3 Wallstreet powerbook with Sonnett G4 500 processor.

I recently installed a Western Digital 120 gig hard drive in an MCE media bay case (replacing a 20 gig). I initialised the disk.

The problem is that when I transfer images to the new disk they are taking up far more space e.g. a 200kb image becomes 3mb. A 2mb psd becomes 10mb.

Have I done something wrong?

Any help will be welcome.

Thanks