There is a firebug that works with Firefox 3, it can be found at GetFirebug.com. The current beta version 1.1 appears to fix a problem that Firebug was having with inspecting anchor elements.

Also, there is a google code project ie7-js. It is a Javascript library that attempts to make IE7 behave more like a standards-compliant browser. It includes a limited PNG transparency fix. It also gives you Pseudo-element like :before and :after.

Combining this with yui and IE7 gets a lot closer to behaving as you might expect!