The only advice I can offer on that is don't do it. Find another solution. SOAP requests from SQL are not recommended, the OLE automation are fraught with problems and then sticking the whole lot in a trigger...
Look at CLR, also consider service broker for async communications. Add a message to the queue in the trigger and let the queue's activation procedure handle the processing.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability