If all the HTML pages are in the base directory, a single line like below would do the trick:

s|(img src=")myserver\.com/|$1|g;

before: img src="blahblah.com/images/pic.gif"
after: img src="images/pic.gif"
[download]

Just run it on each file, and it should be good to go.

When's the last time you used duct tape on a duct? --Larry Wall