Many things will affect your indicated line speed, distance from exchange. local area loading, time of day, and of course Bt's throttling of the lines which they do inspite of denials to the contrary, if you feel your line is not performing as you expected it too, BT will free of charge investigate the problem and let you know the results, but unless there is something the find that might lead to liability cliams against them, they will not make any changes to the download speed and your upload will of course remain static.
I was told quite catagorically by BT that my lines ( I have seven) would give me 8mb 'Under Optimal' conditions yet six years later I still get exactly the same rates at the same time of day as I always did, Not confined to the UK either as family members worldwide have similar problems.
Most generic routers on sale in the Uk will handle these rates with ease, some so called commercial models may give you slightly better connections and clearer signal processing, but other than that Dlink, Lynksys and Belkin are about the best you can buy for around the £30 mark.
Some of the guys in the Yahoo Computer chat lobbies will be happy to walk you through exactly why this all happens and also give you few tips as to how you might get the best from your system.