Since you're going with a Dell, keep an eye on xpbargains.com for coupons. There are often very good deals to be had on Dell (and HP) laptops via discount codes. Pay special attention to the "$400+ off notebooks >$999" type deals. Over the past couple of years I've purchased a couple of Dell notebooks and have saved almost $1,000 off the normal prices by using various coupons from there.
My main home PC is a 1520, and my wife uses a 1420. They're both about 15 months old and see a couple of hours use per day. The 1520 was loaded (w/ 8600GT video) and was about $900 (after saving $450), and the 1420 was about $600 (after saving about $300).
Consider getting a 7200RPM hard drive. My 1520 came with a 5400RPM drive but I later upgraded it to a 7200. It made a difference. Shaved a couple of seconds off boot time, and it seems that the overall system performance is 'snappier' than before.
2GB of ram is the absolute minimum for Vista. Don't do it with 1GB - you'll hate it. I see your configs are both 2+. That's good.
Also think about getting an upgraded video card in whatever notebook you buy, even if it won't be used for any games at all. I actually have grown to accept Vista, but it does need a decent amount of video horsepower to perform as well as XP. I question whether any of the integrated video options can really cut the mustard. My 1520 has the nVidia 8600GT, my wife's 1420 has the 8400GS. I've seen a 1520 with the same processor as mine, same RAM, but with the integrated video instead and it wasn't as fast and smooth as mine. And if you do any gaming at all, the higher-end video cards are a must.
Honestly, I have not been overly impressed with either machine. My first Dell notebooks. They are acceptable and I would say that I am content with them, but they are worth about what I paid. I'd give them a B or B-, if I was grading. I have had a few problems with the notebooks...
The 1420's touchpad is flaky and frequently stops working. It has had strange display driver problems since day one (about twice a month it'll lock up for a few seconds, then report that the display driver is missing/corrupt) and Dell has been useless at offering a solution. And lately, its LCD display recently freaked out and only displayed reds and blacks. A reboot solved it, but I'm leery about that.
My 1520 arrived with a very loose screen that would barely stay open on it's own. I had to take it apart and re-tighten the chassis screws to fix it. NBD, but still sort of a pain on a brand new machine. It's also been back to Dell for repair. About a month before the warranty expired, the LCD backlight/inverter quit and was replaced under warranty. To be fair, the warranty service was very quick - only took about 5 business days. I also replaced the hard drive with an aftermarket one because the OEM was acting up; system lockups, lots of 'bad-sounding' head noise. There was no way to really prove it to Dell so they wouldn't do anything unless it completely failed.
I'm not saying that I won't ever order a Dell notebook again, but if/when I do I will probably cough up the extra hundred bucks or so to pay for the 2 or 3 year extended warranty. I also do know that you do get what you pay for. My work PC is a Dell Precision M4300 'workstation' notebook. It cost work about $2k. It seems better built and more robust than my 1520 and has been a great & flawless notebook for the 6 months that I've had it.
