Smudger - that's fine. Wouldn't stress about an upgrade for a good few years!
Ian - these days it's difficult to go wrong with a PC/ laptop as they're so powerful. Unless you edit HD video and/ or play serious games you'll be fine no matter what. I'd recommend forking out about £400.
A minimum specification for the price would be 4Gb memory, 500Gb hard drive, 15" screen along with a DVD writer. Processor wise I'd lean towards something from Intel rather than AMD but in the end it doesn't matter as it'll do the job you want!