Canon 500d V Nikon D5000?

Which one would "Win" in a head to head.
Cheers

Canon and Nikon are both very, very good cameras.
They will take roughly the same quality pictures and do roughly the same sort of thing, with cameras of this quality it is more about which one you prefer to use.
This is obviously important when using it, you don't want one you aren't comfortable with, for example I'm a Canon fan and have the Canon 550D because I preferred the way it felt to the Nikon even though they do practically the same thing.

My choice would be between the 500D and the new D5100 (not out yet)

The one that would win would be the one that is part of the system I plan on having much later as my photography skills improve.

That means I would be making a choice between the Nikon D3s and Canon 1Ds, Mark III as my end game. If my choice was the Nikon D3s or what comes after it, choosing a non-Nikon would only cost me more money in the end.

You can consider Canon EOS 500D Digital SLR Camera (incl. EF-S 18-55 mm IS Lens Kit)

15.1 megapixel CMOS sensor
Full HD 1080p movie recording with HDMI output for connection to HDTV
ISO range up to 12800
3.4 frames per second continuous shooting mode
Wide-area, nine-point, auto focus system with cross-type central AF point

They are basically the same, i comes down to which you feel more comfortable with. Try to stick with one make as you can build from this.