what will you be using the pc for? if its just browsing the web ect then just upgrade the operating system. but depending if its not that you will be using it for....depends how far you upgrade it.
Surfing the web, some video watching, some actual work (just typing letters0. Don't do a whole lot on computer but I am on it everyday. I just hate typing on laptops. The cost of upgrading to Windows 7 is around $120 and a new PC is around $350.