Looking at the service manual for your computer (available on Dell's website), it shows that your computer should have a PCI Express x1 slot. However, the only way to tell if it is usable is to open the tower and look. The slot can be found in the bottom right corner of the tower. It is the small black slot visible in the pictures shown in your previous thread.
If that slot is open, the card you linked should work. However, be aware that USB 3.0 may or may not speed up your external drive. External hard drives usually have a slow hard drive built into it, and that is the limiting factor for your speed.