Collecting data from remote DBs

Got to start planning for a project that requires our system to collect data from different types of DB platforms remotely from our customers and store them in our SQL DB. Anybody know of any references I could read or where to start with this? I have a couple of ideas, but need to look at all the aspects of this to ensure that it's done correctly.

Thanks.What kind of database? Locating on what platform? How to remotely to access it? Through HTTP or something else?

In general, web service could be a possible solution.|||A couple of our clients are using SQL server, and others are using proprietary DB systems that have XML export capabilities. All are MS based systems and the data collection preference would be via http requests.

Thanks.