questions about which dot net library and methods to use

I need to send XML to a home grown web server on port 80 that "sort of kind of" understands XML serialization.  Will eventually need to be able to write to many of them at the same time. (up to 1000) 

The HTTP protocol for the home grown server is tight and not an issue, but I will need to use  their library for the XML parsing and serialization.

What library/approach for web should I use for the HTTP communication? 

thanks