kat - do you mind if I ask who your ISP is or if you recently upgraded to the latest version of IE?
I have had very similar issues. Intermittently I will get a message about not being able to get to web page. These are usually sites I have not had issues with before, and visit frequently. It asks me to do a little connectivity test which is always fine. It seems to have started only after I "upgraded" to IE8. I should mention that my current system is an old POC (piece o' [blip]).
(I intend to replace it in the next couple months). I have been thinking it is my computer that was the issue. But your post really made me wonder since it sounds so similar to what I have been experiencing.
I do not have wireless, but Qwest DSL. Mine is a desktop, not a laptop. Sometimes just refreshing the page works. If not, I usually have turn the modem off and on again then I am fine. Occasionally I will have to clear my cache and restart the entire computer to get everything functioning again.
I don't know which it is.
Qwest ISP, my obsolete system, or glitches with IE8? Or a perfect storm of all 3.