To test certain functionality in B2B I use VMWare. This is very convenient because you do one install in your VMware Image and then just bring it down, zip it for archiving and copy it for having two instances.
Doing so I have two VMWare images with Integration B2B in it. When you have a 2GB computer and set memory settings of the guest OS to 850 MB you can startup the two instances on your computer together. I agree it is not fast, you have to accept swapping on your host and guest OS but it works. Of course it is very convenient if you have 4GB in your computer.

There are however some things you have to arrange to get it working properly.

1. Network settings
Take care that both the VM's have a host-only adapter. When start the guest-os after the copy VMware will ask you to create or keep the system-identifier. Let it create a new one, since it is in fact a new computer. If you're using Linux as a guest, you'll have to probe it for a new mac-adress. If you have RHEL4.0 with gnome, you can do that via application menu> system settings>network. Double click on the device (it is probably inactive), choose the hardware device tab. You'll see a "Bind to MAC address"-field with a probe button at the right of it. Click on the probe button and after that you can activate your network device.

Determine the ip-adress of your guest OS-es. If you're using Windows, you can do that with the ipconfig command in a command-window. Under Linux you can do it as root in a terminal window with the command ifconfig. Be sure that you use the right ip-address, the one that is coupled to your VMWare host-only network. It is convenient to have the ip-addresses added to the /etc/hosts file of the guest-os'es as well as your host. Under Windows you can find it in c:\windows\system32\drivers\etc. Under linux of course it is /etc/hosts.
Choose a smart host name, for example rhel40-b2b-acme and rhel40-b2b-globalchips.
Having it added to your host's hosts file, you can use these names to connect to your b2b servers. When you use firefox (or if you really insist internet-explorer 7.0) you can open up the UI's of both servers then in seperate tabs.
Check if the machines can reach each other by doing a ping.

2. Change the server name of your Apache
When you do an install of the Oracle Application server the installer will fill in the server name of the server at install in the httpd.conf as a servername. This is pretty inconvenient in that when you try to connect to your server using your new hostname (as filled-in in your hosts-file) Apache will respond by filling in the servername in the URL. Firefox will then do subsequent requests to the original servername that may not exist in your hosts-file. You can solve this by changing the servername in the httpd.conf file. This file is found in /Apache/Apache/conf. Look for the parameter ServerName and change it to the name you've given it in your hosts-files.

3. Copy your configuration.
The above steps you'll do if you want to use two B2B to test the internet based protocols like ebMS. In that case you'll need two servers (or you'll have to use som kind of driver java-application). When you build up an agreement with quite a lot of business actions, you probably consider to do this twice. Since at one B2B you'll do the configuration but need a complementary setup in the other B2B. Since the Initiating Capability at the first B2B need the complementary Receiving Capability at the other B2B. And ofcourse you'll have to setup the agreement and all the businessactions and document types. To at least prevent doing the business actions and document types twice, you could do the setup at one site and export and import it at the other site. Then you can delete all the supported business actions and agreements (but ofcourse not the business actions and document types). And then add them correctly again (in the complementary way).

But I figured: lets try it the "nasty way". Do the configuration at one site and import it into the other. Open up an sql-tool and connect it to b2b user in the infrastructure-database of the second B2B install. Query the table tip_party_t. You'll then find the parties that you configured. Also you see one party that has the ISHOSTED column set to 'Y', the other ones have an empty or 'N'. Update the two parties that you want to switch: update the one that has to be 'host' to 'Y', and the other one to 'N'. Then click on the Trading Partners tab in the UI of the B2B and you'll see that the other party has become hosted.
The pitfall that you have here is that you are probably logged on as admin . This user is coupled to the party that used to be the hosted party but now is not. When you purge the repository and log off, you would not be able to logon again, because this user is deleted.
So in the UI go to the new hosted trading partner and then to the "users" tab. Create a new user name it "admin-host" (something else then "admin") and add the "administrator" role to it.
Now you can logoff and logon using the new user again. Then you can delete the admin users at the original tradingpartner.

It should not be necessary to mention that switching host-tradingpartners like this is not supported. It is just old-school hacking your way through the B2B repository. But hey, you did copy/archive your Virtual Machine, right?