Im not sure if it will come formatted as FAT32. They usually don't say, but it will either be FAT32 or NTFS.
If you buy it, connect it to the PS3. If it is detected, you're good to go. If not, you will need to attach it to a PC.
I have a youtube video you might find helpful. A link to the software needed to format the drive is provided in the video description.
When shopping you will find some drives formatted for Windows and some for Apple/Not Windows.
That means Windows formatted is NTFS, other will be FAT32.
Note FAT32 only supports disk files up to about 3.3GB (I can't remember actual size). Windows can happily read FAT32 and NTFS, but you can't copy large files (> 3.3GB) from your Windows PC to the external FAT32 drive.