Hi, I am LOOKING to get this Sound-CARD for my PC - http://www.asus.com/Multimedia/Audio_Cards/Xonar_DG/
But looking at the connectors on that PCB it doesn't look like the PCI cards I have SEEN, I know it says that it requires PCI 2.2, But I am unsure about what this means. 

Here is my PC - http://www.dell.com/us/dfb/p/optiplex-755/pd - Desktop Version, not MT, SFF or USFF 
This is the Motherboard - http://www.blueskyave.com/servlet/the-1612/DR845-Dell-Optiplex-755/Detail 

Just need to know whether this would work in my system as I have one similar to this - http://www.ezcomputers.co.uk/sound-cards/778-6-channel-pci-sound-card.html - which stops my PC from booting, but when I take it out the PC boots as normal. The PCI slots are fine as I have tried a Wireless PCI 'N' Card successfully. 

Thanks.  http://www.soundonsound.com/sos/may07/articles/pcnotes_0507.htm
The Xonar DG is compatible with both 5V and 3.3V PCI slots. It will work with your PC.

Quote

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!