I am totally new to building computers based on a dualboot Windows / Mountain Lion configuration, and I am currently totally confused which graphics board to get that supports four displays under Windows, and at least three under MacOS Moutain Lion simultaneously, preferrably two via Display Port, and the rest via HDMI or DVI (or mixed).

I wanted to get an ATI Radeon HD 7770, but I already found out that Mountain Lion does not support this, so which card in this price range (arount 100) can you recommend, that works flawlessly on my new system.

By the way, the rest of my components will be, can you take a quick look and check if they are okay? But most important is an advice for a suitable graphics board:

1 x Western Digital Caviar Blue 1000GB, 64MB Cache, SATA 6Gb/s (WD10EZEX)
1 x Samsung SSD 840 Series 120GB, 2.5", SATA 6Gb/s (MZ-7TD120BW)
1 x Intel Core i5-3470, 4x 3.20GHz, boxed (BX80637I53470)
1 x G.Skill DIMM Kit 8GB PC3-10667U CL9-9-9-24 (DDR3-1333) (F3-10600CL9D-8GBNT)
1 x HIS Radeon HD 7770 GHz Edition iCooler, 1GB GDDR5, DVI, HDMI, 2x Mini DisplayPort (H777F1G2M)
1 x Gigabyte GA-Z77-DS3H, Z77 (dual PC3-12800U DDR3)
2 x Dell UltraSharp U2412M schwarz, 24"
1 x LG Electronics GH24NS90 schwarz, SATA, bulk (GH24NS90.AUAA50B)
1 x Cooltek K3 Evolution USB 3.0
1 x be quiet! Pure Power L8-CM 430W ATX 2.3 (L8-CM-430W/BN180)