Hi Elliot
Unfortunately that's never going to work.
The siteurls.config file is used for rewriting. So while the
parameter looks very tempting, it's not actually for redirecting.
To redirect in DotNetNuke, you have to use the 'permanent redirect' option, which will redirect a url matching a DNN page to any other Url. So if you had a page called 'PressCentre' you could redirect it to the PressMediaCentre page.
However, on top of that, in order to get /presscentre to work, you have to switch off page extensions, which won't work with the standard DotNetNuke Url rewriter. Because otherwise only /presscentre.aspx will work.
The solution? Well the only way I know of is to purchase my module called 'Url Master', which will both allow you to switch off the .aspx, and to redirect the /presscentre Url as you wish to do.
It's all detailed here:
Creating a Url with no aspx extension on your DNN site
and
301 Redirect a Url to a DNN Page
There may be other ways to achieve this in DNN, but (obviously) this is the way I would do it.
regards
Bruce