I have a 1tb mybook that I've sectioned off into a 750ntfs/200F32. I don't have problems with my PS3 seeing the drive, but as most have said, you must use the triangle to actually see what's on the drive.
Also, I have noticed that my PS3 doesn't like to do a firmware upgrade from the Ext. HDD, I always have to use a flash drive.
I know how to solve this problem. I reformatted my external HDD one time. (STUPID DECISION ON MY PART) but yeah in order for the HDD to be read by anything it has to formatted to master boot format. Here is a link to a DIY guide. It includes instructions with pictures on how to format a drive to the partition type you need. It should work.
The western digital my book II 500 GO works great in USB