idk, those prices you put up for some of those parts seems steep. i think youre just looking at the wrong "bargain" components. you can get a nice antec case for that same price, which will probably be quieter and cooler than that piece. not one of the huge towers, but antec has some nice smaller cases nowadays. also if you really want to upgrade from your current setup, your either going to have to wait for AMD to make a pci express board of buy a new LGA 775. because although your 5200 isnt super good, its not teribly bad and without spending large amounts of money on the aging AGP technology, it is hard to upgrade. just some meat to chew on for you.
-Epox EP-8KRA2+ with KT600 VIA chipset
-Athlon XP 2500+ Barton core
-160gb WD SATA
-Nvidia 6600GT agp
-1024 Mb Dual Channel DDR PC3200 corsair valueram
-Antec 430 Watt Truepower
-Windows XP Pro OS