Even with the above error, I was able to get this working just fine.
The installer did not create the virtual directory for the LanSweeper website so I had to go in and create that manually. I also then had to install the ASP.NET AJAX 1.0, available here: http://www.microsoft.com/downloads/details.aspx?FamilyID=ca9d90fa-e8c9-42e3-aa19-08e2c027f5d6&displaylang=en
After this was done, I restarted IIS and still had a server error. I had to convert the virtual directory to an application. To do this, right click on the virtual directory in the Internet Information Services Manager and then select convert to application or something along those lines.
My directions above should be the steps necessary to get the LanSweeper website up and running. I am doing it all from memory (without looking at my Win2k8 server) so they may be a bit off. Please let me know if you have any further questions or need any assistance. I'd be glad to help.
Regards,
-Aliby