>> I am planning to put flash ... inside the pageheader
If you put Flash inside the header, then I don't know you and you shouldn't expect any help
_Please_ don't do that.... (for so many reasons, too many to list here... just don't do it...)
>> I am planning to put image inside the pageheader. But if i put a larger image, then it overlap the menu area. I am sure that the resize solution is in css.
It is indeed CSS.
>> May i know which css to look for?
Impossible to say without an example of what you are doing.
>> by default the web server put the styles as custom.css. But custom.css is not in the application working directory.
Correct. I don't ship that file - it's there for you to put your own custom css into. (you create the file, add to it whatever you want, and so on.)
>> The menu procedure mention something about the following css 'nt-site-header-6 ui-widget-header ui-corner-top' but where is it located?
The shipping CSS is in the "styles" folder. In a variety of files. Also in the \Themes\whatever folder. but you should not edit any of these files, you should put your edits in your own custom.css.
Cheers
Bruce