Does the Dell you mention has something like Front Row and the remote? Has Dolby 5.1 audio so you can connect it to your Home Theater?
Modern Windows notebooks have been coming with HDMI outputs since the Santa Rosa platform was introduced, and even some before that.
If you look at the MacBook, you need a mini-DVI to DVI connector, a DVI to HDMI connector, and then you need an optical cable with a mini-TOSlink to TOSlink adapter.
Then you have to connect the HDMI cable to the TV or receiver. If you connect it to the receiver, then you have to go through the trouble of setting up the receiver to accept audio from the optical cable rather than the HDMI cable which, on some receivers, is next to impossible or very difficult to do.
It's basically the same for the MBP, you just need the DVI to HDMI adapter instead of both it and the mini-DVI adapter.
With the Dell (and others) you get HDMI. You just plug the HDMI cable into the computer, plug it into your receiver, and you're good to go. HDMI passes both digital video and digital audio over one cable. If you're watching DVDs, it will pass the Dolby Digital and DTS signal to the receiver for decoding.
Also, if you have one of the modern dedicated GPUs (even the lowly GeForce 8400M GS that Apple should put in the MacBook), that HDMI output will be HDCP certified and the GPU will have full hardware support for VC-1 and H.264. Meaning you can get an HD DVD, blu-ray, or combo drive that does both and use your notebook to play HD movies on your TV.
Windows Vista Home Premium and Ultimate both come with Windows Media Center. Sorry, but Media Center simply blows away Front Row in terms of looks and functionality. You can get yourself an analog, or digital, or both, TV Tuner in ExpressCard or USB form and (assuming its a Media Center tuner) it will have the full "Media Center" remote, which includes a breakout box with IR blaster that can take full control of a digital cable or digital satellite box. Or it can pull in OTA HD signals.
Media Center really is a great program, especially for recording TV. I use it with DirecTV. I have XP MCE 2005 on my HP (very similar to Vista Media Center, minus the much prettier eye candy) and the HP ExpressCard TV Tuner with the USB breakout box for the IR Media Center remote and IR blaster that controls my DirecTV box. While I'm gone, I just set the HP to fall asleep after 1 minute, after setting up the TV shows I want recorded. During the day, or whenever, it wakes up and records the show and falls back asleep after 1 minute.
Front Row is more like an extremely limited preview of what Media Center can do on Windows.
Plus, if you're using it for DVDs, the built-in DVD decoder in Vista Home Premium and Ultimate takes full advantage of GPU video features. So you get full hardware MPEG-2 decoding, deblocking, hardware upscaling, etc. Essentially, the image quality blows away what you get in Front Row or DVD Player as long as your Windows system has a modern GPU (again, the lowly GeForce 8400M GS that Apple should put in the MacBook can do this, but OS X would have to be reworked to finally take advantage of these features).