I'll go ahead and provide some more "in-depth" instructions on telling GNS3 to use a "remote hypervisor" (a dynamips instance listening on another machine).
You can even use this setup with Amazon EC2 (or another utility computing provider). A setup with a utility computing provider would also be extremely useful for testing out topologies with a very large number of routers, to see how OSPF may behave at scale, etc. I've documented how to do this at my last job (but this was before GNS3 was so popular) and we used it successfully for numerous scale tests. This would also be ideal for folks that don't want to spend the money on a high-end server but can afford to spend a few dollars for a few hours of "server time" for GNS3 labs, without chewing up CPU cycles on their home machines.
The following instructions assume your remote hypervisor is running Linux.
Step One: Set up your Linux box.
jjensen@jjensen-dev:~$ mkdir dynamips
jjensen@jjensen-dev:~$ cd dynamips
jjensen@jjensen-dev:~/dynamips$ mkdir tmp
Step Two: Set up GNS3. Edit -> IOS images and hypervisors. Click the "External Hypervisors" tab. Add in the IP address info for your remote hypervisor (Most of the time you can leave all the fields besides IP address as the default). Once you've filled in the IP of your remote hypervisor, click "Save".
Once you have your remote hypervisor added, go back to the "IOS images" tab and add in IOS images. There are two important bits to remember:
Use the "Linux format" directory notation (see screenshot), and make sure that the "use the hypervisor manager" checkbox is unchecked so that you can select the remote hypervisor that you just added. When adding the IOS image with the remote hypervisor, make sure that your remote hypervisor is selected.
Once you have your IOS image added, start up Dynamips on your remote machine.
jjensen@jjensen-dev:~/network_eng/dynamips$ sudo ./dynamips-0.2.8-RC3-community-x86_64.bin -H 7200 &
You should now be able to add devices to GNS3 topologies on your Windows machine, and GNS3 will communicate with the remote hypervisor on another machine. You also get the console access via PuTTy and such for free as well. Note that there isn't really a "configuration limit" on how you want to add your IOS images and hypervisors. You could even have it so that you have a separate remote hypervisor per IOS image if you wanted. Pretty powerful stuff.
If anyone could add additional answers on how to make this work with JunOS/"virtual" Olive, I think that would also be pretty useful. :-)