For the web you're fine but obviously not everyone runs windows so you'll want some backup fonts in your font-family style.
Using fonts in other documents is different. If you go to the fonts directory, right click on a font and go to the details tab, it tells you about the licensing stuff (Even though I can't resize the window to actually see all of the text. -1 points for MS).
The "font embeddability" part says whether or not you can embed the font in a document. With nearly all the standard fonts this will say "Editable", meaning that you can embed thte font even when the document is editable by the end user. Occasionally, you might see a font that doesn't allow you to embed at all or that allows you to embed but only if the end user is not able to edit the document.
The "License description" tells you more but it's cut off on my computer so I don't know exactly what's there other than "you may use this font to display and...". Not much help but maybe there's a way to read the rest.
That said, I'm sure you could get more info from a quick google than you could from the MS details window.
I worked at a company that chose Zapf Humanist as their standard font without looking at the licensing. They had no idea what they were doing so even though they used it on every document and all the employees had it installed on their computer, they didn't know how to embed fonts and virtually nobody outside the company had it so all our documents showed up with Times New Roman or something when clients looked at it. When I told them nobody could see the font unless they revisited every doc to embed it and that they were using it illegally anyway and would have to pay for the license, they changed it pretty quick. And this was at a fairly big company with nearly 400 employees. Crazy.