Paula-
I love my Dell Inspiron notebook with Windows XP and 15" screen. I always buy the "refurbished" models at a discount. These are systems that have been returned for whatever reason. Anything wrong gets replaced before shipping out, (so effectively, they've been tested twice, not just once), and the warrantee is still 3 years, just like the "new" ones. Never had a problem. Oh, actually, one time the modem wasn't working. Literally the next day a new one was on my doorstep via FedEx. Same with a hard drive that I lost to the trojan virus. Had a new one arrive in one day and they helped me install it on the phone.
Unless you process video daily, I can't see why you would switch to Mac at this point...you probably have all Windows software already. (I believe the whole "Apples are easier" line is just a marketing thing. I've had jobs where I had equal access to both machines, and found myself always choosing the PC over the Mac. They both have learning curves, they're just different. I find Macs as frustrating as some find PCs, so it's all in your frame of reference.)
For the record, I generally run several high memory programs simultaneously (Dreamweaver, Photoshop, Word, Firefox, Flash, etc) and almost never crash.