From my experience it can be done with the right program. However sometimes HD's when creating more than 1 partition can be a bit funny about recognizing a new FAT32 partition created out of an existing NTFS partition. Sometimes you get lucky depending on the external and how it is recognized but their has been a time when I was required to wipe the entire drive in FAT32 first, then resize the partition and add the NTFS partition. Then all of a sudden my PS3 recognized it.
So anyway outside of my storybook above, the program I recommend 100% is called Acronis Disk Director. Great utility just to have on your PC. Its so easy you'll freak and no you will not lose your data as long as you don't do something stupid. I have not tried the other one that was mentioned. You just have to resize your NTFS to something smaller, then you will have ullocated space, then you select the unallocated space and create a FAT32 partition on it. Woala! Then hope your PS3 sees it, if it doesn't you may need to try to format just the FAT32 with another utility like SwissApps. If that doesn't work read my storybook above and copy my steps. Note- you will probably need to back up everything before you do that though. If you want to keep your stuff currently on there. And always read carefully with either of these programs if you have data you want, human error can be a b%@tch!! Ive goofed it with these before not reading thoroughly. Luckily I had a backup of my data.
Another good program sometimes I use along with Acronis is Swissknife Apps. This program works well to assure you a get a FULL FAT32 format. Sometimes I run it once on my PS3 partition just to make sure. FAT32 can be a little quacky from my experience mostly with just how you format, partition, how other things recognize it, etc.
As far as I know, my ps3 has never had an undetected error.