Too many Mac buffs these days paying for overpriced soda cans =[. I would stay away from Macs. You can get the same components in a PC for a much lower price, and if you have the ingenuity, you can install the OS.
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Anyway, to answer your question, I want to first start off with the difference between the Dell models "Studio" and "XPS."
The XPS line is recongized as Dell's "highest end model," just under their Alienware Subsidiary.
Studio is the next best line that lies right in between the Budget Inspiron line and the XPS High end line. Studio is for people who want a little more power than the Inspiron, but don't want all the bells and whistles of the XPS line.
As you can see, this kind "quality" is reflected in the relative prices.
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Both seem fine to me for use at college. You've gone for the right choices in screen size. You don't want to go any bigger than 16" when you want to be carrying it around.
Let me tell you not to buy the M1330 to start off. The laptop was released in 2007, and it is thanks to the M1330 that you get the styling and design you find in the Studio series.
With that being said, the M1330 has components that are a bit old and not quite worth the sale price listed. The CPU might be a tad faster because you have more Cache, but the video card is on par with the Studio 15's.
The M1330 is using Centrino technology while the Studio 15 runs on Centrino2. The different isn't huge, but it allows for slightly faster speeds (as you can see in the RAM MHz) and a better integrated Intel graphic solution.
Also, the Studio 15 has a bigger screen, which you might to be great when you're viewing pictures or watching Videos. However, this takes a bit away from the portability.
RAM helps the processor run programs. The more ram you have, the better able your processor will be able to manage loads. Three or Four GB of RAM is usually the standard and is quite sufficient. If you want to go a head and spent a tiny bit more to upgrade to 4GB RAM, it wouldn't be a bad idea. However, 32-bit windows vista can only support up to 4GB of ram, so I wouldn't advise getting more than 4GB unless you plan on paying extra for more RAM and switching to 64-bit windows vista.
If it were up to me, I would grab the Studio 15 with the video upgrade to the ATI HD 4570. You get a bit more for the same amount of money.
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If you're looking for alternatives in your price range, you might check out HP. There are also lesser known manufacturers that make great spec laptops for under $1000: a few of these can be found here: << http://www.newegg.com/Store/SubCategory.aspx?SubCategory=32&name=Laptops-Notebooks >>