I couldn't answer your question regarding how Dell/Windows 7 handles the multimedia. Outside of making a custom ringtone from an existing mp3, I simply don't use my laptop for that purpose.
I use my Dell for programming in SQL and a custom PeopleSoft application called PeopleTools. I can tell you that I've had a session of Toad open and connected to 3 databases, along with PeopleTools, while running a copy of FireFox, and a copy if Internet Explorer, and I've had no slowdown.
When I got my new laptop last March, I had been dealing with Toshiba, and how they had my laptop for 2 weeks before replacing the screen (when I opened my laptop, the screen shut off - if I kept it at about a 30 degree angle, it would turn on, so I knew it was some loose connection or something - nothing wrong with the motherboard). I simply can't be without my laptop that long for work. I had a coworker who's motherboard was fried on her Dell, they had a technician come to the hotel that night and swap it out.
So the differences between Macbook and Macbook Pro? First, the size. Macbook is available in one size only (13"). Macbook pro (13", 15", and 17"). Comparing the 13" macbook to the 13" pro:
Height: Macbook 1.08 inches (2.74 cm) vs Macbook Pro 0.95 inch (2.41 cm)
Width: 13.00 inches (33.03 cm) vs 12.78 inches (32.5 cm)
Depth: 9.12 inches (23.17 cm) vs 8.94 inches (22.7 cm)
Weight: 4.7 pounds (2.13 kg) vs 4.5 pounds (2.04 kg)
Last April, I bought my wife the 13" macbook pro. My wife liked the look and feel of the Macbook Pro, and I wanted to get her 4GB ram. (I think the macbook comes standard with 2GB). Harddrive size they are similar, so that's a wash.
I'd say if you want something that looks sleeker, is lighter, then go with the pro.