(URI) In C#, how can I make it so it ends .aspx like a directory? Like file.aspx/programtorun/

(URI) In C#, how can I make it so it ends .aspx like a directory? Like
file.aspx/programtorun/

So I've been using php, and switched to ASP.NET because I love it.
Anyway... I've been developing my own website and such, but I cannot
figure this out for the life of me!
What I have:
string val = HttpContext.Current.Request["Header"];
// filename: index.aspx
// what I need to get
if (val == "random")
{
renderA.Random("randoms.html");
}
else
{
renderA.Index("index.html");
}
What it returns in the URI
/index.asp?random
What I wish it would look like:
/index.aspx/random/
Is there someway I can fix this problem?