Since your desktop is a PC, I recommend you to stick with Windows. It'll be much easier to link them in a network (for file sharing and printing).
Also you had a Dell before, that was a good choice, stick with it. I use Dell too (for many years), they have great products and when you have trouble, their support is the best. Keep an eye open for promo's on their website, could save you some money.
Are you planning on gaming or image processing (like photoshop etc.), then you'll need a decent graphics card. Otherwise, you'll be fine with a powerfull processor and 4 or more GB of RAM
link to Dell's laptop search site.
happy hunting