I just looked at my site (http://softserv.ca) on a laptop and the background images used along the top and top-right looked horrible -- very grainy and striated. It was IE8 on XP. I couldn't check the screen resolution, but it didn't look like anything out of the ordinary.
I'd like to know what typically causes such striation, and also, I know there are tools out there for testing cross-browser. What are the best ones? Thx
Adobe Browserlab is a good one, and for testing screen resolutions, Viewlike.us.
These are my favo(u)rites.
You could use a virtualization product such as VirtualBox or VMWare to setup configurations for every target platform you want to test. The disadvantage is the lack of automation, but you can easily adjust screen resolution and snapshot various configurations without needing to buy a ton of hardware.
VirtualBox 3.1.x supports branched snapshots, which makes it efficient to keep copies of operating systems with different configurations and patch levels.
Browsershots used to be really great, with testes from almost all known browsers. It used to have even the website sourcecode in a svn repository, but it's kind of abandoned these months.
The browser screenshots still work though. You may give a try.
The guys from doctype (check SO footer) are behind litmus, a great application for compatibility tests. If you want something more professional, I would go with them.
Browsera is a cross-browser testing tool that will compare layouts across different browsers and detect problems automatically.
As for commentary on what causes these issues, check out the QuirksMode site.