Your Iframe HTML will probably look something like:

<iframe name="FRAME1" src="id77.htm" width="730" height="360" framebor
+der="0"></iframe>
[download]

You need to pull out those iframe elements and do another LWP::UserAgent::get on the src attributes. It is a bit like writing a script that reads a webpage and does stuff with the images. However instead of an image you have another round of HTML to parse. I am not sure what you mean by "almost simultaneously".