I've actually installed it remotely at my hosting provider.  It is challenging but can be done.  Here are a few suggestions that might help with your issue.

1) Find out what user your DNN install is actually running as.  To do this I created a text file in the root folder of my installation and renamed it user.aspx.  Inside the text file I had a simple statement: <%=Environment.UserName%>.  This returns the username of the process that you should be concerned about.

2) Next I granted that username "Full Control" to the approriate folder/files.  If you can do this at the root foler level -great! If not, here is the list - bin folder, config folder, desktopmodules folder, portals folder, web.config file, and siturls.config.

3) When granting permission be sure and check the little box that says "Apply to all child objects" or on some systems "Replace all permissions on child objects".  Otherwise your permissions change will only apply to new files..

Hope this helps..

Oops - I forgot about that.  I think all you need to do is temporarily rename your web.config to web.config.old.   This will turn off the DNN httpmodule that tries to run/parse urls for any .aspx page.  Then run the user.aspx file. After you determined the user that your process is running as - be sure and rename the web.config.old file back to web.config.   I've experience many diverse types of errors installing 4.02.  I've installed it about 15 times now.  If you want to send me a screen shot of the particular error you are getting then I may be able to help you faster. I'm not sure if they allow email addresses in this forum .. just incase my phonetic spelling is: noel-at-foutsfamily-dot-org.  I'd love to help because I've beat my head up against a wall myself on this install serveral time.. but I've always learned something.

If the user is Network or ASPNet.  Then it could be the level of trust your ASP.NET site is running at Full trust level - not medium.  You can find this setting in the <trust> element of the machine.config file.

Noel