A 2nd hand laptop, amd athlon 64 and 2gb ram will do fine on win xp or more than enough for ubuntu.
Around £150 for laptopp, plus free office software (openoffice) and avast for antivirus. More than enough
Running similar spec pc, bit old but use it for video conversion and decoding and games
Stay away from Dell, pc world and norton. Coming from a IT Technician