so if i want to make a background to a layout, what size should i make it?
& im not talking about a pattern background. im talking about like a background with pix of me & stuff like that =)

Well it depends on what kind of look you want. The widest I'd make it is 1000 pixels, just because many people have a 1024 x 768 browser. What I suggest is make a background image around 600 x 600 pixels, but make sure that the background image's color matches the background color of your xanga... that way when the background image stops, it does look cut-off. After that, place it on the bottom left or right of your screen, and adjust the position and width of your module/blogs so you can see the image and your content at the same time.

depends. are you submitting this layout? or are you making it for yourself? if you are submitting, i agree with digitalfragrance, however, if it's for yourself, go with what looks best on your screen.