well it's standard, but the case itself, the board is mounted upside down, so the CPU it pointing downward, expansion cards are pointing up, power supply is up in the case, and some things are proprietary such as the front I/O board for buttons, THOUGH you can still use the "Front LED" headers which contain HDD led, Power led, power switch and reset switch headers/pins.
So finally i'm using a 2-Molex to 1 PCIe 6-pins, and a 2x PCIe 6-pins to 1x PCIe 8-pins, for the video card, since it's a tailored PSU, it have a lot less cables than standard ones you buy in stores.
So i was able to fit my Scythe Ninja plus. Rev.B on that Core 2 Quad Q6600, and i may try to fit my Thermalright HR-05 on the chipset someday.
I had to remove a big foam block on the back of the board in order for me to fit the board inside the case, i guess this block was used as a support in the XPS case which must have a deeper back case.
So yes, the Dell XPS 630i motherboard is a standard ATX board, but you need to figure out the pinouts for the power, reset switches, and power and hdd leds, shown on the "my630i.com" website.
But fitting a large LGA775 cooler is a pain in the ass, but i guess it's pretty much the case on ALL boards, except coolers which size/width doesn't go over the push-pins. Good thing i kept all brackets for this cooler!
Though i'll have to wait till my friend bring me his 4 x 2gb DDR2-800 because it's a pain to install patches with 1gb DDR2-667 on Windows 7...
Case: Antec Three Hundred (w/ Corsair TX650W) | Main Board: Asus P7P55D-E LX | Video: eVGA Geforce GTX 560 Ti SuperClocked 1gb | HDD: Western Digital WD10EALS | CPU: Intel Core i5 750 (w/ Prolimatech Megahalems rev. B + Nexus B/W 120mm @ 12V). | Memory: 4 x 2gb G.Skill DDR3-1600 | Exhaust fans: Noctua NF-S12B FLX @ 12V. & Noctua NF-P14 FLX @ 12V. | Monitor: Asus VE228H.