Hello again,
I am currently in the planning process of developing an application that I would like to expose the data from across multiple platforms using SOAP/XML web services.
I am developing the application using asp.net 3.5. Any links or good tips for getting started would be great!
Cheers
Microsoft (and hopefully the majority of .NET developers) are pushing for more adoption of WCF as opposed to old school ASMX style ASP.NET web services. You might want to consider exploring your options with WCF.(Link is a beginner's guide)
If you're using asp.net 3.5, your best bet is to go with WCF to create your services.
Take a look at this SO post for good WCF References:
By all means, check out those beginner WCF resources!
There's the MSDN WCF Developer Center which has everything from beginner's tutorials to articles and sample code.
Also, I would recommend you have a look at the Pluralsight screen casts on WCF - it's an excellent series going from "Creating your first WCF service" and "Creating your first WCF client" all the way to rather advanced topics. Aaron Skonnard very nicely explains everything in 10-15 minutes screencasts - highly recommended!
If you're into reading books than I can recommend:
Programming WCF Services: http://books.google.co.uk/books?id=DW2ldput788C&printsec=frontcover#v=onepage&q=&f=false
It's on Google books so you'll be able to read large chunks of it online which should get you a good taste of it.