http://www.soundonsound.com/sos/may07/articles/pcnotes_0507.htmThe Xonar DG is compatible with both 5V and 3.3V PCI slots. It will work with your PC.
However, when the PCI specification was updated to version 2.3 in 2002, while it continued to support both 5V and 3.3V keyed-system board connectors, it ceased supporting cards that require 5V signalling, only supporting 3.3V and Universal expansion cards. This means that although the PCI expansion slots in a new computer may look identical to those of your previous PC, and physically accept 5V-only cards, if the motherboard is running PCI version 2.3, only cards that can run on 3.3V signalling levels will actually work — most confusing!
Explains why the older, non-universal sound card you have isn't compatible...