Not entirely sure what you mean by 'an off camera flash' - could it be that that you are wanting to use your current flash off-camera?
Based on the assumption that it's the latter, then I also assume that you are aware that if you own the 580EX Canon flash unit (not sure about the xxx model) then you can trigger this off-camera using the cameras in-built flash so long as the in-built flash is 'looking' at the red panel on the front of the off-camera flash unit. In this instance the off-camera flash needs to be set to 'slave' with the in-built flash as 'master'. Whilst in the most part this works OK indoors it has limitation outdoors because bright sunny conditions say can overpower the in-built cameras flash output so that the slave unit doesn't see it.
By far the best method (although not cheap) is the use of Pocket Wizards which use radio signals and are also versatile, reliable and easy to set up. Rather than go into a lengthy description, take a look at this short tutorial video which will give you the idea much better than reading about it -
http://www.pocketwizard.com/inspirat...ction_mini_tt/ .
A couple of points worth noting: there are alternatives to the Pocket Wizards which I have read from time to time on other forums which are considerably cheaper by all accounts. I personally believe that if something is 'too cheap' then it's probably either cheaply made, lacks in overall functionality or is otherwise missing something. A sceptical approach I know but that's me.

The other thing worthy of note is that whatever you buy that is electrical always ensure it has the CE designation - in other words approved for use in Europe. There is always the risk of one piece of apparatus using radio signals actually interfering with another piece of equipment and in the case of the Pocket Wizards (like a lot of other things) the radio frequency used varies from market to market.