For Vista, look at the MS requirements…and double it at least and make sure it's certified. Triple if you can afford…then Vista should rock your socks. If you learn how to use it, Vista features and technology blows XP away…when it works. ;) You want it to last so get 64-bit Vista Home Premium or Ultimate. It’s mega-fast with 64-bit apps as well as lets you upgrade > 4GB TOTAL RAM (system RAM + graphics card + other devices).
But if you have old programs, they might not work (esp. with 64-bit version). Google “Vista compatibility list”. Knowing a bit about computers helps getting the old problematic ones to work (Internet has a lot of solutions that smart people share).
Ultimate is the best but if you don’t think you need anything that fancy, Home Premium is good too. Get a good video card if you want Aero graphics (at least 256MB 128-bit in the newer cards). Better if you can afford.
Vista uses extra RAM to store commonly used files in a new activity known as “disk caching”. The computer uses artificial intelligence to determine which files will be used most and copies it to RAM (where it is much faster than accessing your hard disk). This includes components of the programs you use on a regular basis. When you need more RAM for programs you launch, etc. the computer purges the “least likely used” files from RAM to make room for the new program. That’s why if you look at the performance monitor, Vista always has near zero “free” RAM. So in theory, the more RAM (for disk cache) you have, the faster your computer will operate. This can also be augmented (to a lesser effect) with a USB flash drive with a technology called ReadyBoost. Just stick it in and select “Speed up my system” and leave it there.
Vista Home Premium and Ultimate has Windows Media Center, where with a TV card/USB adapter (if not integrated) of the type that fits your TV/Cable, acts similar to TiVo. You can play your videos, schedule recordings, etc. You can get a wireless keyboard / mouse or gyro-mouse and it will be sort of like remote control. If you do this, get a big Hard Disk.
Vista supports touch-screens and voice recognition if you’re into note-taking and dictation. A good program to use with this is OneNote, which is included in some Office editions.
Deals of America and Tech Bargains catch good deals on HP and Dell’s and sometimes you can get like $500 off! XPBargains has deals and coupons on Tablet PC’s!
Unless you are an artist, most Universities (and programs) as well as the rest of the world use Windows. WinMacs are popular but for the price, Macs don’t run Windows as well as other brands, but sometimes it doesn't really matter that much to most users. In addition some just want it for fashion and like them to match their iPods.
Macs are durable because many have an accelerometer in there that can "increase the chance" of saving your hard drive when you drop it. Like those used in airbags. The power cord is also magnetically attached so it reduces the chance that you yank it off the table.
OSXMacs can exclusively install Final Cut Pro (which is good for media work). Adobe CS is also good and available for Windows but works better on OSX. The Windows version actually looks like an OSX port. Many OSX keepers are artists as usual. Emotion workers are generally not as good with computers as logic workers so OSX is good for them. Because it’s less complicated and harder to mess up, a lot of computer newbies also use Macs and you will see a lot of “Get a Mac! They are so awesome!” without any technical explanation to back up that opinion. ;)
Mac Pros:
OSX stability
OSX is easy to use
Dual-bootable to Windows
More durable than many brands
Trendy
Mac Cons:
Not as much peripheral support
Not as much software support
Windows doesn’t run as good
Expensive
Minority
Windows PC Pros:
More customizable
More choices
More styles
Cheap hardware
Vista has best gaming capability (Direct3D 10)
Windows PC Cons:
Less stable (unless you are an IT pro)
Many are relatively not as fashionable
Not as user-friendly
Some extra features in Windows requires advanced knowledge to use
The extra features require better hardware despite your use of them or not
Details of features can be found here:
http://en.wikipedia.org/wiki/Windows_Vista
http://en.wikipedia.org/wiki/Mac_OS_X
Some brand statistics: In terms of recent sales, the top 3 manufacturers are HP, Dell, and Acer (Gateway). Apple is #4 in USA.
http://community.winsupersite.com/blogs/paul/archive/2008/04/24/mac-q1-2008-market-share-3-26-percent-worldwide-6-26-percent-in-the-us.aspx
Pretty good deal on a powerful laptop: $900 - Gateway M-6851 NoteBook Intel Core 2 Duo T5550(1.83GHz) 15.4" Wide XGA 4GB Memory DDR2 667 250GB HDD 5400rpm Dual layer DVD Burner ATI Mobility Radeon HD 2600(512MB GDDR3 Dedicated Memory)
http://www.newegg.com/Product/Product.aspx?Item=N82E16834101154
Pretty good deals on mid to powerful Tablet PC’s: $700 - Gateway C-141X / $1100 - Gateway C142XL
http://www.gateway.com/systems/series/529597319.php?mtr=DCYAONANC&sg=hm&ph1=8667187749