Actually, what is your "mypage"? Is it a folder, a .js file, a .php file or other things?
You may find the following directive of apache suit you:
By the way, I found the following directive in xampp httpd.conf:
Alias /webalizer "C:/xampp/webalizer/"
Options Indexes MultiViews ExecCGI
AddHandler cgi-script .cgi .exe
Allow from all
It may help...
For your 2nd question, you are of couse not able to access phpmyadmin unless you put phpmyadmin under htdocs. However, if you don't want to put it under \htdocs, you can use the above "Alias" directive to map your phpmyadmin to other place.
Hope the above helps...