It really comes down to what you used to create your pages with. I use Dreamweaver with mine, as well as Xsite Pro. A good rule of thumb is to preview new pages or sites in both IE and Firefox (Flock will look the same as Firefox).
Most of the headaches I ever had was when I was using Frontpage. Whatever it is you're using you might need to redo some of it with different software. There's a few free ones out there to try out. NVU is pretty popular
http://www.nvu.com and I know that a couple of people in here use other free ones too.
I have to say though, from a KISS principle side of things, a marketers best friend is Xsite Pro. It does a great job on small sites selling info products, just isn't that cheap.
Cheers,
Nez