Hi there and welcome here.
You can try some of the cheat codes in the readme file on the iso / live dvd and a text editor to read from this file. Notepad or similar.
Sounds like it needs a driver or a cheat code to bypass this. Boot time currently is about max 2 mins so if going past this and still nothing then try the cheat codes. You could even remove the pci cards and then try to boot likely one of them wants a specific driver but this way you know what is causing it and can easily find the correct fix for it.
Then at boot menu of the live dvd use up down arrows and press F5 to show text at the bottom.
Then add say "xdriver=nvidia res=1680x1050 dodmraid noacpi " or similar. Some pc's / parts needs extra stuff to boot from. ALso check the wiki top right of this page for help and the search or at gentoo.org forums / wiki you should be able to get info for the specific motherboard as well.
Someone with similar parts will post here soon just hang in there and try some of this.
Hope this helps
It could be the build in nvidia 6100 video card needs to be deativated in the bios ?
or just boot with the inbuild video card and later once ready add the 8600gts not sure here.http://usa.asus.com/products.aspx?l1=3&l2=101&l3=345&l4=0&model=1647&modelmenu=2