[quote name='Buuhan1']Where's the deal? Gotta buy all your programs and OS.[/QUOTE]
Gotta does not exist in the world of wants.
[quote name='SEH']Only if you want to go legit, and even then, there are ways to get stuff on the cheap. I believe you can still get Windows 7 for $30 if you have an .edu email.
That said, if you intend on paying for an OS as well as stuff like Office, building a PC for $400 or under would be pretty tough. If you intend to go the "free" route for your OS and whatnot, building a decent/good PC for $400 or under would be a breeze.[/QUOTE]
I would not advocate for someone to get their software illegitimately.
Now sure which OS the OP is looking for but you can buy a brand new copy of Windows XP Professional in several places all over NYC like 'Strand' book story for as low as $13.
If you are in college or know someone in college they can get you a copy of Windows 7 for $29.99.
http://www.microsoft.com/student/en/us/software/windows.aspx
As for Office related software I would go with Open Office...outside of it being free there is no difference between it and Microsoft Office.
http://www.openoffice.org/
If you have no problems with DIY then I would suggest you hit this CAG thread were vets of putting together machines assist each other with critique and links to better and better deals...reviews and such...
http://www.cheapassgamer.com/forums/showthread.php?t=226363
I personally never spent over $400 for a computer in my life. So the deals are out there it's up to you whether you want to build the machine and put in the effort to get those deals.
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Below is my current main rig.
CPU: AMD Phenom II X3 720
MB: MSI DKA790GX
RAM: Kingston HyperX 4GB
Videocard: HIS Radeon 4870 512MB
Hard Drive: Western Digital Caviar 500 Black x 4
PSU: Rosewill RP550V2-S-SL
Case: Antec Skeleton PC Case
OS: Windows XP Professional SP 3 (Gamer Edits) and Ubuntu 9.10 (Gamer Edits)
NO DVD Drive, NO CD-ROM - I do everything via USB or download.
Total cost after rebates and coupons: $188.93