The photography world is pretty well dominated by Apple Macintosh ® systems at this point.  However, if you do not want to use or cannot afford a Mac, most (if not all) of the software used by photography professionals is also available for Microsoft Windows ®.

That said, your first choice of computer as a photography student should be an Apple Powerbook ® notebook computer.  As an alternative, you could get a lower end Apple notebook or a Windows based notebook.  See the general Student Computers page for reasons to buy a notebook.  An additional advantage for someone involved in photography is that you can have your computer with you on a photoshoot.  This is invaluable, as you can hook most high end cameras directly to your computer for image capturing.

Recommended system specifications:
You will want a system with a good amount of system memory.  Preferably, at least 1 Gigabyte.  This will allow you to manipulate large photos with having your computer slow down as much. 

A faster processor should be a secondary consideration - it will be quite helpful, especially when you are applying filters to large photos. 

A large hard drive is the another thing you should consider.  Raw photo files are quite large in size, and you will want to keep multiple versions of each photo, so you will quickly fill up space.

Also, be sure to get a system with at least a CD burner on it, if not a DVD burner, so you can cheaply store old files, and backup your current work.

For software, hands down you will want Adobe Photoshop, if not the entire Creative Suite.  This is by far the most popular photography program out there.  Check out what other woftware your school uses.  You'll also want some sort of photo capture program, but this will likely come with whatever digital capture device you purchase.

Last, it could be worth it to invest in a color correction device and software, to make sure what you are seeing on your screen is the same as what will come out on your printer.  For instance, we use the EyeOne Pro from GretagMacBeth.