Break it down into pieces thjat either you do know haow to do, or can work out. If those peices are too big, break them down until you get to somethign you can do, or can research how to do.
Your task is already broken down into major modules:
1) Send commands via email to a remote system
2) Turn message body into xml
3) Execute command from xml
4) Send the result back to the source.
So, look at the first one: do you know how to send an email?
Hint: if you look here http://www.codeproject.com/script/Articles/MemberArticles.aspx?amid=6122202
] under tips you might find something kinda useful...
Once you get started, it looks a lot easier, it's just that you are bogged down by thinking of it as a single task.