xml and asp.net are different things. Xml its self is not really a server side language, there are no scripts. Infact xml is a markup language... extensible markup language. I use xml with asp.net, but I use xml mainly for configuration. Xml can also be used for data storage, rss, soap, etc etc etc.
Canging a .asp extention to a .aspx extention will fail. Asp and asp.net run differently, they are fundamentally different. For instance all of the languages used to do asp.net are oo, none of the languages used to code asp are oo. Asp.net can not be done in vbscript, its done in vb.net. But asp and asp.net can run side by side so you do not neccessarily need to change all of the files at one time.
They should still work just fine.
jscript cannot even be used to do asp.net. Jscript.net is available, but the support (you will not find many articles) for that is very lousy because it is not a commonly used language. I would say c# is your best bet because it is very popular and has a similar syntax.
w3schools cannot help you anymore, atleast not for asp.net. W3schools does not talk a lot about code there, their asp.net section is lousy. I love their asp section and their html and css stuff, but their asp.net is basically nothing. A good site to go to is www.4guysfromrolla.com , they have tons of good stuff. Their articles are very very well written.