External HDD Booting Problems in BIOS

I've searched the forums and can't seem to find anyone with this specific issue. I have two different Dell laptops, an XPS M1330 and an Inspiron e1705. I have an OS installed on a full size Seagate Freeagent 320GB external drive and it runs swimmingly. My BIOS detects it on both systems and boots straight away.

In an effort to have a more portable version (This drive is rather large, and has a huge base and a power supply) I bought a 500gb external Simpletech portable drive. Neither BIOS can see this drive. It doesn't have a power supply, but does have a Y connector so two USB ports can provide power. When I plug the drive in while in windows or OSX, it recognizes the drive straight away, as does Disk Manager in windows. The drive works fine.

I had this same problem with a 16GB Patriot USB stick I bought with the same purpose, neither computer would recognize it as a USB boot device.

Again, I can boot from USB without issue using other devices, just not these.

Is this a USB power issue? Dell "Premium" support provides no help here, they say "interesting" and that's about it.

Any thoughts?