There are lots of CFD and spread betting providers that will allow you to open an account with them. I prefer to use a UK company, they are better regulated and less likely to be taken for a ride. Just google them. I'm not entirely sure what rules apply to those of you that are not UK based.
If you have never done this before then I would suggest that you try and open some form of limited risk account. I think the charges are slightly higher, but at least your wont lose your home, wife/husband over it !
Remember investing is always risky business and the only people that normally make money from it are the fund managers, banks, investment houses. Joe public is not supposed to make any money from investing.........and this is the reason I think I can do a better job that these corporates who seem to get paid whether they make anything or not !