Ah, i see. Masking and non-masking reaaly means framed and non framed. Framed means that you (or script) create top frame that does not contain any info and lower frame with 100% width and height of site where do you like you visitor will be redirected.
This is a simple example code:
Code:
<FRAMESET border=0 frameSpacing=0 rows=*,100% frameBorder=0 cols=100% MARGINHEIGHT="0" MARGINWIDTH="0">
<FRAME border=0 name=123 marginWidth=0 marginHeight=0 src="http://www.yoursite.ru/blank.html" noResize scrolling=no TARGET="123">
<FRAME border=0 name=1234 src="http://www.somesite.com/index.php?fromyoursite" noResize TARGET="1234">
Using this code you just shade real site as address bar stays does not change and stays on yoursite.com
Nonmasked - it's simple Redirect instruction. Redirect are very often made via 302. That's not so good. You should type yoursite.com and see HTTP headers to see what code use your hoster or registrar.
Normally you have to choose - PR with 301 redirect and light to real location of pages or doing nothing with PR with shade to real location.
Try read
http://www.corpsstudio.com/l1_Domain_Name/301_Redirects_and_Search_Engine_Optimization_.html may be this will help.