I think you'd be the first if you made a package that can
- Scan a web site for resources
- Validate HTML
- Validate CSS
- Validate JS
- Find Broken Links
I can think of a couple of ways to do some of those.
You might be able to use HTTrack or other website copier to scan for resources.
HTML validation could be done with this tool: WDG HTML Validator (has a Validate Entire Site option)
There's a Microsoft plugin for IIS - Search Engine Optimization Toolkit, it can scan a given site for broken links (along with several other pretty nifty site stats)
Can't think of any that will validate CSS and JS while scanning an entire site, modern web design practices usually yield a small number of JS/CSS files anyway so you may be fine one-offing those in some circumstances. I can see potential for a need to scan inline JS/CSS though.
To assist you in developing such a tool you could download the source for
W3C Markup-Validator: http://dvcs.w3.org/hg/markup-validator/
CSS Lint: https://github.com/stubbornella/csslint
JS Lint: https://github.com/douglascrockford/JSLint