Hi,

If you're using .NET 2, you can try to get the Web Service Security
Guide (MS_WSS_Dec_05.pdf).

Found on msdn:
http://www.microsoft.com/downloads/details.aspx?FamilyID=3e02a6c8-128a-47c2-9f39
-4082582f3fe1&displaylang=en

If you find interesting ressources on that, it could be interesting to
list them here as well.

I hope it helps, don't hesitate to ask again if not. The more precise
the questions, the easier it usually will be to answer.

Reguards,

You could also use WSE
http://msdn.microsoft.com/webservices/webservices/building/wse/ which
implements WS-Security (an international standard) to secure your web
services.

Josh
http://www.thejoyofcode.com/