I have, in the past, had similar problems with webpages not being able to be displayed. This is usually down to 1 of 2 problems. Firstly, your ISPs DNS server is down, in which case you will just have to be patient and wait until it comes back up. The other possibility is that you may need to go into your firewall's configuration and manually grant the executable, 'iexplore.exe', access to the Internet. Of course, with IE8, you need to be aware that it is a Beta product and that there may still be bugs in the code that can cause problems for some people with certain hardware configurations. If this is the case, then by providing feedback you will bring it to the attention of the development team which will assist them in the further development of the program.
Incidentally, I am using IE7 but will switch to IE8 when the final version is released.
4 x 4GB DDR3-1600 Corsair Vengeance CMZ8GX3M2A1600C9B (16GB)
Graphics card(s)
MSI GeForce GTX770 Gaming OC 2GB
Sound Card
Realtek High Definition on board solution (ALC 898)
Monitor(s) Displays
ViewSonic VA1912w Widescreen
Screen Resolution
1440x900
Hard Drives
OCZ Agility 3 120GB SATA III x2 (RAID 0)
Samsung HD501LJ 500GB SATA II x2
Hitachi HDS721010CLA332 1TB SATA II
Iomega 1.5TB Ext USB 2.0
WD 2.0TB Ext USB 3.0