web services without upseting current set up

Hi people:

I was wondering what are your views, on which is the eaisest way to
develop web services that either doesnt upset your current set up (ie
no changes to server, config files, etc) or that changes it very
little (ie no need to instal 53 plug ins and change ports ,etc ).
and keeping the easy bit going.

I m gonna be using some xml-rpc and soap
I would really apreciate the input
Cheers

Jo

.