cheap build need help plz

this is the exact motherboard i have out of this pc
http://reviews.cnet.com/desktops/hp-compaq-evo-d510/1707-3118_7-20719371.html

i want to add a decent graphics card 2 gb memory and a better processor and bigger hd. im very good with hardware problems ect. but when it comes to building a pc i have never fully built one i dont know what is compatible with what i want this pc mainly for gaming and watching movies so can anyone list some good parts or what i should be looking for cheers

Do you want a new case two, also what size ATX or micro ATX.

yeh i was guna get a nice case with a few led fans and stuff i think atx im not sure not all clued up on it.

What is your budget.