I have used flash(.swf) animation & high quality graphical image there in my vb.net application. But problem is that sometimes when I click on menu it shows small line under it & take time to load it. It shows line under menu when load another forms though there is no line under that menu. I have 25 forms & every form has high quality image(image size is 1280*1024). Is there any way to get rid of this problem? Is there any way to make my application smooth though its high graphical & animated? Please help me.

Unfortunately, using heavy graphics and in such sizes tends to slow things down a bit.
I have a friend who did the same thing in her application. And it was sluggish even on my, high-end, computer.

For the large, I'm assuming, background image I recommend that you pick a solid color background and use pictureboxes for the details.
Those pictureboxes can be moved on the z-axle so that they appear behind all other controls. Right-click on the picturebox and select "Send to Back".

I'm not entirely educated regarding flash animations, but I think others would agree with me that they too consume a fistful of CPU power.
So you should keep those at a minimum as well.

When all is said and done, your application may look cool as hell.
But what's the point when you can't run it properly?