A PC or Laptop puchased in 2007 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:

Windows Vista  http://www.microsoft.com/windows/compatibility/windows-vista/default.aspx

Windows 7  http://www.microsoft.com/windows/compatibility/windows-7/en-us/default.aspx

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 Windows 7 (also see my Windows 7 page):

http://windows.microsoft.com/en-us/windows/downloads/upgrade-advisor

Second-user a budget around  £150.00 - £250.00 should be sufficient to purchase an entry level PC Tower Unit and TFT 17" Flat Screen Monitor, which is running Windows Vista or Windows 7. 

Please note that a PC or Laptop with either NT4, 98SE, Millenium Edition, Windows 2000 or Windows XP should be avoided.  

I charge £60.00 to install a Customers  "Legimate 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 7 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.