I've written a block called 'EmbedWebPage' which does simply that- it downloads a web page and puts it into a block.
It's been tested on 1.8.2+, and doesn't require additional database tables. I can't see why it wouldn't work in other versions (it simply uses the php function file_get_contents() to download the web page).
Any suggestions are welcome, feel free to use it at your own risk. I do recommend testing it in a test environment first, but it's up to you.
Installation instructions are included in the readme file in the zip file attached, but it's really the same as any block installation.
Hope it helps!