OK I can usually take the "techie" stuff and explain it to the non-techie people. I've been using PCs (that's windows) for 10+ years and switched to a Mac a few months ago. I LOVE IT.
Here's what you don't need to know: Windows is an operating system that runs on PC's. Mac OSX (10) is the operating system that runs on Macs.
Here's what you need to know: You will have to adjust to the new "layout" of a Mac. Programs are in a different spot. Menus are a little different. BUT - I bet that new Dell has Vista on it. Vista is a version of Windows. Most computers had Windows XP which is what you are thinking of. Windows "Vista" is completely different. No matter what, you will need to learn a new way to navigate your programs and files. This is a great time to switch.
Macs cost a little more because they have better parts. You can get a cheapo version of a PC. You can't really get a cheapo version of a Mac. They don't build junk.
Software is complicated. Most everything you need comes built in. Email, Internet Browser, Photo Editing (iPhoto is AWESOME - you plug in your digital camera and it just figures it out.) You can still use Microsoft Word, but you have to buy a special version. You can buy different word processing software that will probably be cheaper and better.
It took me a while to adjust to the difference, but now that I have, I can see that the Mac is better. Windows overcomplicates things. My only problem with it was MY adjustment, not the computer itself. Now I'm a fan.
Oh - most importantly - the Mac almost never crashes. And it turns off and on REALLY quickly. And my Macbook weighs less than Sammy.