Using XML with PHP

Hi,

I'm trying to intergrate an XML data feed with an existing website to
provide currency conversions.

The rates will need to be stored in a MySQL database after the feed's
been updated by XE.com, the site will then access all of the rates via
the MySQL table.

I'm having problems figuring out how to get the rates into php and then
into a DB, i've tried and succesfully created my own RSS feeds which
are then read into PHP, this all seems quite easy, but it's just not
playing ball for me.

If anyone has any advice on where to start it'd be greatly appreciated.

Kind Regards,

Ian