I was looking around to see if I could find a cheap way to work on my Switching lab either for CCNA or CCNP but for me CCNP. I found on Dynamips/GNS3 site this link to a tutorial.
I looked at 3550s and 3560s. The cost of 2 3550s would be $1,000.00 USD on ebay..not tooo bad but I am cheap sucker. So I believe you can run the IOS on your PC with Dynamips. It will look like or actually from my understanding and experience you will be using telnet (putty.exe) to run real IOS images.
Also, look at IOS helper program on google to find and buy it, there you can get IOS images with the program and pull down from some remote ftp server in Russian (always virus check your IOS images after download) sometime viruses show up in them. and then you can run real IOS images in Dynamips..