for that u have to put one dll file in your project and some change in web.config file. aspnet_isapi.dll. add this file.
<configuration>
<system.web>
<urlrewrites>
<rule>
<url>/urlrewriter/show\.asp</url>
<rewrite>show.aspx</rewrite>
</rule>
<rule>
<url>/urlrewriter/wohs\.asp</url>
<rewrite>show.aspx</rewrite>
</rule>
<rule>
<url>/urlrewriter/show(.*)\.asp</url>
<rewrite>show.aspx?$1</rewrite>
</rule>
<rule>
<url>/urlrewriter/(.*)show\.html</url>
<rewrite>show.aspx?id=$1&cat=2</rewrite>
</rule>
<rule>
<url>/urlrewriter/s/h/o/w/(.*)\.html</url>
<rewrite>/urlrewriter/show.aspx?id=$1</rewrite>
</rule>
</urlrewrites>
</system.web>
</configuration>
<configuration>
<configsections>
<sectiongroup name="system.web">