A few questions.......

As you may have noticed, I've posted a few topics here - I promise this is the last one (for now)
Anway, before I go off and buy upgrades for my system, there are a few things I am unsure about.
1. If I buy a motherboard supporting DDR2 RAM, can it take ordinary DDR?
2. The motherboard I am considering buying says it takes RAM speeds DDR2 533, 667 and 800. Will a 900Mhz stick (http://www.ebuyer.com/UK/product/116782/rb/0) work on this board?
3. The motherboard it ATX format, will this fit in all ATX cases?
4. The motherboard comes bundled with an AMD X2 6000+ processor (@3Ghz), which has L1 Cache 128Kb L2 Cache 2x256Kb. Is this better than an AMD X2 5600+ with L1 Cache 128Kb L2 Cache 2x 1Mb (@2.8Ghz) - I need to know which to get. Link to motherboard CPU bundle: http://cgi.ebay.co.uk/AMD-6000X2-AM2-DU ... dZViewItem
5. Does the 8800GTS 640Mb version use 2x PCI? If so is it 2x PCI express or 1x Express and 1x 32 bit? Also, which brand of card is best?
6. Will a 550W PSU take all this (with 4 case fans, and a huge amount of room inside for air circulation)
Sorry for asking so much - but I'm not great with the latest PC stuff :-?
Thanks
Anway, before I go off and buy upgrades for my system, there are a few things I am unsure about.
1. If I buy a motherboard supporting DDR2 RAM, can it take ordinary DDR?
2. The motherboard I am considering buying says it takes RAM speeds DDR2 533, 667 and 800. Will a 900Mhz stick (http://www.ebuyer.com/UK/product/116782/rb/0) work on this board?
3. The motherboard it ATX format, will this fit in all ATX cases?
4. The motherboard comes bundled with an AMD X2 6000+ processor (@3Ghz), which has L1 Cache 128Kb L2 Cache 2x256Kb. Is this better than an AMD X2 5600+ with L1 Cache 128Kb L2 Cache 2x 1Mb (@2.8Ghz) - I need to know which to get. Link to motherboard CPU bundle: http://cgi.ebay.co.uk/AMD-6000X2-AM2-DU ... dZViewItem
5. Does the 8800GTS 640Mb version use 2x PCI? If so is it 2x PCI express or 1x Express and 1x 32 bit? Also, which brand of card is best?
6. Will a 550W PSU take all this (with 4 case fans, and a huge amount of room inside for air circulation)
Sorry for asking so much - but I'm not great with the latest PC stuff :-?
Thanks