One feature of GNS3 that you might like to explore is the fact that if your physical topology includes some of the routers and interface options supported by GNS, you can use GNS3 to test various versions of IOS. The trick here is to know which version of IOS is suitable for your needs. The cisco Feature Navigator (available at http://tools.cisco.com/ITDIT/CFN/jsp/SearchBySoftware.jsp) can help, but in many cases you can often work out if an IOS image you are using supports the features you need simply by looking at the IOS name. Here is a way to decode image names.
Firstly, you have to understand the groupings of letters in the IOS name. They consist of up to seven major fields followed by a
[Platform]-[Feature Set]-[Memory ...