$750 for tower with monitor, OS, KB, and mouse? KB and mouse I will leave to you.
CASE: http://www.amazon.com/Technologies-Source-210-Computer-Black/dp/B005869A7K/ref=sr_1_1?ie=UTF8&qid=1324896021&sr=8-1
CPU+RAM: http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.782522
MOBO: http://www.newegg.com/Product/Product.aspx?Item=N82E16813131767
HDD+PSU: http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.785486
GPU: http://www.newegg.com/Product/Product.aspx?Item=N82E16814102908
DVD: http://www.newegg.com/Product/Product.aspx?Item=N82E16827135204
LCD: http://www.newegg.com/Product/Product.aspx?Item=N82E16824009306
OS: http://www.newegg.com/Product/Product.aspx?Item=N82E16832116986
About $777.
Can't afford? Get the http://www.newegg.com/Product/Product.aspx?Item=N82E16814102940 instead