xml feeds system for vacation rental listings

Need a system that will read xml feeds from various partners and save them into our database. This is for a vacation rentals [login to view URL] that those properties show on our site and respond/integrated to our search box, so that new owners can continue to register and seach our site . We will define all fields for our partners, some will be optional, others will be required. I will give you the xml feed list once the bid is accepted. There are about 40 to 90 fields that we collect. The feed system will also need to download images(urls perhaps) for each listing and save that into our file system and into a mysql table with dimensions, file extension, etc. The feed system should be able to detect changes in a listing provided by a partner and modify it in our database. It should be able to detect deletions as well as new additions without re-importing all listings every time