Hi Ella,
At the £500 mark you have a fair amount of choice. There are plenty of good spec laptops that will handle heavy business use, as long you don't need them for high drawing packages, such as CAD programmes.
We have a couple of suggestions for you:
For £449 you can get the great Toshiba A300D-13X which comes with an ample 200GB Hard Drive, 2GB of memory. The Toshiba also comes with the powerful AMD Turion 64X2 Processor TL60 that will ensure great multitasking performance.
Another great branded laptop inside of your price range is the Sony VGN-NR38M/S. this machine also has 2GB of memory but has a bigger hard drive (250 GB) The Sony comes with the Intel Pentium Dual Core processor T2390 which like the AMD in the Toshiba is a great processor for multitasking.
Both of these machines come with Windows Vista which is now compatible with the majority of existing software, but if you are already dependent on any particular a quick check to see if it is Vista compatible would be wise. There is a link below to microsoft where you can check your software, though this list is not exhaustive.
Hope this helps, and all the best with your laptop, whichever one you decide to get.