SSRS has a full SOAP API, you can see info on that here: http://technet.microsoft.com/en-us/library/ms155376.aspx
From the above article:
// Create a Web service proxy object and set credentials
ReportingService2005 rs = new ReportingService2005();
rs.Credentials = System.Net.CredentialCache.DefaultCredentials;
// Return a list of catalog items in the report server database
CatalogItem[] items = rs.ListChildren("/", true);
// For each report, display the path of the report in a Listbox
foreach(CatalogItem ci in items)
{
if (ci.Type == ItemTypeEnum.Report)
catalogListBox.Items.Add(ci.Path);
}
There's a full tutorial there too: http://technet.microsoft.com/en-us/library/ms169926.aspx