I have a server where I am running several domains, so I redirect to folder for each.  How can I determine and set the directory? 

For example, I use a VBscript asp file to redirect to the folder for webs based on domain:

Case "www.domain1.com"

Response.Redirect "web1\index1.aspx"

Case "www.domain2.com"

Response.Redirect "web2\index2.aspx"

end select

The redirect, however, doesn't retain the path, so the next click has a path error.

How can I insure the right path?

The following works great in classic ASP, haven't tested w/ .NET (Gut feeling that it should work fine) 

// Assign SiteNameURL to Server variable

SiteNameURL = request.servervariables("HTTP_HOST")
SELECT CASE SiteNameURL
CASE "www.domain1.com" Response.Redirect "web1\index1.aspx"
CASE "www.domain2.com" Response.Redirect "web2\index.aspx"
END SELECT 

Well, one way is to make sure all your pages only do relative linking. link like /Web1/blah.aspx is strictly forbidden, use blah.aspx instead.

A second way is to employ a routing engine in the ISAPI layer or HttpHandler / Module layer. 

SiteNameURL = request.servervariables("HTTP_HOST")

it will result to domain1.com not www.domain1.com

so check the condition according to that  

Arent you using wrong path?

It should be Response.Redirect "web1/index1.aspx" insted of Response.Redirect "web1\index1.aspx"

Note the change of "/". URL accepts "/" and not "\". It doesnot matter you work in Windows or linux platform.

this is what I'm doing, thanks for validation!

after I do response.redirect, I only route with next.aspx, not web1\next.aspx

so, say path for routing is "http://domain.com/index.asp"  this page just does redirect per script, such as "web1\index.aspx" 

the problem is, it's not retaining the web1 folder as part of the path for the next click, so it's trying to access http://domain.com/index.aspx not http://domain.com/web1/index.aspx

it's loading the first page, so the redirect is working.  we are not at the URL level, it's in a VBscript, thanks.

 Try take a look at this blog entry from ScottGu

http://weblogs.asp.net/scottgu/archive/2007/02/26/tip-trick-url-rewriting-with-asp-net.aspx