Wow, that's still only about enough for (if we're lucky) 3 games. Which is way different then when I put in a 250gb HDD in my Xbox and had 5 xbox games, several anime series, a lot of roms and music and still had 100gb left. In fact, I hope there IS a hack to allow the use of external HDD.
if your talking about the ps3 theres no need for external
http://ps3.qj.net/Like-the-manual-said-PS3...pg/49/aid/72455
Things needed for Replacement
Replacement HDD (2.5", SATA) LAPTOP DRIVES..
Phillips and slottet head drivers (+ and -)
1.Turn of the console, lay it on its sides, and open the lid labeled "HDD"
2.Remove the blue screw once the lid is open.
3.lift the handle and slide it to the right gently.
4.Remove the 4 silver screws from the sides
5.The model of HDD is Seagate's ST920217AS.
6.Install the Replacement HDD back onto the frame, screw it back, and slide the HDD back into the console.
Slide it to the left until you can feel that it's been connected. Screw the blue screw back in, and close the lid.
7.Restart the PS3, and the console will ask to Format the HDD. Choose "Yes".
8.Replacement HDD is recognised instantly.
looking further down in the article
DailyTech already attempted to use a 3.5" 320GB hard drive (with some creative cabling), and had no problem utilizing the new drive.
now microsoft better wake up and do the same, 20 gigs is nothing.