Changing Permalinks leaves my site wrecked…

hey,

i am facing a very big problem…

i am using wordpress 2.9.2 on my windows server 2008/2003 hosing with PHP 5 and MySQL 5…

if i use the default permalink my site works…….
but the moment i change it to something else even in the list provided my site doesn’t load…..

i guess it is some .htaccess file problem but i really dont know what it is…..

and i need to change the permalinks……

so what should i do to get my site loading????…..

and please explain me in depth as much as possible cause i dont understand HTML and PHP, however i understand some code and Java……

Please Help Fast……

Thnx…….