I am currently running both the 32 bit and 64 bit versions of Windows 7 Beta and have had no significant problems running dual monitors.. I do have to admit though on the 64 bit version it took a little more time to get both up and running properly but with a couple driver "tweaks" it's fine now...
Primary display is Samsung 22" LCD (T220) Secondary is a NEC Multisync LCD1700M+ (an oldy but a goody none the less, I use it mainly for surfing/working with apps when I'm watching a video on the primary display)..
The video card in my main comp is listed in my system specs but it's a Radeon HD 3870 512MB..
Operating System Windows 7 Ultimate 64- Bit Edition
Computer Type Custom Build 6 of 6
CPU Type and Speed AMD Phenom II X4 965 (3.4GHZ) 4000MHz HT Quad-Core Socket AM3
Motherboard Chipset Asus Crosshair III Formula AMD 790FX Socket AM3
System Memory Type Corsair TR3X6G1600C8D Dominator - DDR3-1600:PC3 -12800 - 6GB - Non-ECC Unbuffered 240-Pin DIMM
Video Card Type and Speed Sapphire Radeon HD 5870 1GB PCI-Express (2.0)
Computer Monitor Samsung SyncMaster P2350 23" FULL 1080p HD LCD Monitor
Hard Drive (2) WD VelociRaptor 300GB 10000RPM 16MB Buffer: (2) WD Caviar 1.5TB "IntelliPower" 64MB Buffer
Optical Drives (2) LG 22x Super Multi Drives (SATA II) - Both with Lightscribe
Network Adapter Asus Crosshair III Formula Gigabit Ethernet Adapter
Anti-virus Software AVG Free Edition 9.0
Computer Skill Level Self-Taught Expert
Windows Experience Index 7.2