A PC or Laptop puchased in 2006 or later should be capable of running Windows Vista or Windows 7 (may need a memory upgrade, 1GB is minimum, I would recommended 2GB), if you have existing hardware and software then check out Microsoft's compatibility pages:

http://www.microsoft.com/windows/compatibility

Pre 2010 NetBooks generally run best on Windows XP Home and whilst Linux is also offered, it is not compatable with Windows software, Windows 7 is currently replacing XP Home, as the standard Windows Operating System.

Fortunately Microsoft do provide an on-line advisor tool to help with deciding wether a PC or Laptop meets the requirements to run Vista or Windows 7 (also see my Windows 7 page):

http://www.microsoft.com/windows/products/windowsvista/buyorupgrade/upgradeadvisor.mspx

http://www.microsoft.com/windows/windows-7/get/upgrade-advisor.aspx

Second-user a budget around  £125.00 should be sufficient to purchase an entry level PC Tower Unit and TFT 17" Flat Screen Monitor, which is capable of running Windows Vista/7 and software like Word, Excel, Irfanview/Gimp (Photo Editing).  A PC or Laptop with either NT4, 98SE, Millenium Edition or Windows 2000 should be avoided.  

I charge £60.00 to install a Customers  "Legimate Windows XP, Windows Vista or Windows 7 Operating System" (this includes all drivers and updates), or having purchased a New PC/Laptop charge £40.00 for initial configuration.  Though if you want a Custom PC built I charge a fixed fee of £100.00 plus the cost of hardware and software.

New Windows Vista PC Towers & Laptops and TFT Monitors  are available from Retailers Comet, Argos, Tesco & Staples, though please contact me for advice as I may be able to locate from Internet eCommerce Resellers at lower cost.