If I preview my web-application in Internet Explorer, everything is fine... if I preview in Firefox, the control buttons below - "SAVE", "PRINT", "CANCEL" overlaps one another... Why is that? Any way to rectify this problem?

Tried using CSS?
Personally i prefer to code the entire xHTML/HTML output myself. Assign classes and use an external stylesheet. I'm not sure if this is how ASP.NET 2.0 does things, but ASP.NET 1.1 used embedded styles in attributes which sucks for many reasons.

I did an ASP.NET application for my college assignment without any user interface problems. I recommend previewing in Firefox first, then IE. From experience, IE first just leads to alot of broken layouts in other browsers.

CSS can adjust control placement on a form? Well, in my codes, I already set absolute position already but preview in IE ok, in Firefox not ok.

Can gimme a sample of positioning with CSS?

like to change font type = font-family

To change position, how?

Have you try to use 'HTML 4.01' in 'Target Schema for Validation'?

Dont know what's that dude... care explaining?

Well, if you double click any *.aspx file, on top left there's a drop down list (hover your mouse on it the tooltips mention 'Target Schema for Validation').
lf l'm not mistaken the default is 'Internet Explorer 6.0'. So, in your case change that to 'HTML 4.01'.

Hope, that's help.