$700 is a bit more than a budget computer...
You have an OS to install? At least until Windows7 comes out?
I would go with the following (order of your list)
1 - Case: Pretty much anything that is Rosewill = crap. Want a good basic black case with good airflow, try this:
Antec 300 $55 -
http://www.newegg.com/Product/Produc...82E16811129042 (IS your PSU 24pin and 4pin wires very long? Many of todays cases such as the 300 has the PSU on the bottom)
2 - Keyboard, $7 keyboards won't last long. A good cheap keyboard is an HP or Logitech for $15+ But none of them are as good as what was made 10-15years ago.
3 - Spend $40~50 more on a 24" Samsung. Acer tends to be washed out. Over at Costco, they sell the 24" Samsung for $200. $250 with HD-Tuner and HDMI input. (Add $50 from newegg)
http://www.newegg.com/Product/Produc...82E16824001280 http://www.costco.com/Browse/Product...=1&topnav=&s=1 4 - With AMD DDR2 boards, its generally best to go with DDR2-800mhz: RAM 4GB DDR2 800 - $47 -
http://www.newegg.com/Product/Produc...N82E1682014518 G.Skills are good, I use them.
5 - Mice : Check out Logitech... $5~10 mice tend to live for a month or so. Spend at least $15+ Good mice are $30~50.
6 - Motherboard The 790 doesn't have onboard graphics. Not sure what you're asking. If you buy a motherboard without on-board graphics and you don't add a video card, you DON'T get video. If you buy a motherboard with onbaord graphics, you do. Here are two ATI 785G boards with onboard video... they are quite good. Cost less, just as fast and newer than the 790.
MB Gigabyte 785 $90 -
http://www.newegg.com/Product/Produc...82E16813128395 (ATX 2x 16x slots)
MB Gigabyte 785 $80 -
http://www.newegg.com/Product/Produc...82E16813128394 (mATX)
Your 500w OCZ PSU is good enough for ATI 4850 and 5700 series video cards. I'd go for a 5770 or 5750 which comes out next month.
So spend a bit less on the mobo and case, put a bit more money on KEY / mouse and monitor. A 24" screen is sweet.