I've sent you a nice long email on all of this, but at present you have an annual investment allowance of £50k with which you can claim up to 100% of your first year purchase of computers, furniture, equipment etc. providing the total doesn't go over this. Then in subsequent years you can claim 20% of the cost as a capital allowance as a writing down allowance (
some reading)
This is set to change in April 2011. I think it was brought in during the recession to help businesses a bit. I'm guessing it'll go back to how it was before ie. 50% of the cost in the first year, 40% in the second year.
For travelling, train fares, bus fares, hotels and food purchased, if all in the name of the business are then expenses. For cars, note your mileage and you can claim 40p a mile. If you have a passenger in the car you can claim an extra 5p a mile per passenger.