please help...speed drops

i recently got 128k up/ 512k down aDSL. its the fastest available in my small town right now. last night i did the CNET bandwidth tester. it said i was hitting 473Kb/s. today i got my router and hooked it up and split the internet to my computer and my brothers. the other is just sitting there with no activity. i tried the bandwidth tester tonight and it says i'm only hitting 84.3Kb/s. my download speeds also dropped from 55 Kb/s last night to 40-43Kb/s. what the hell happened to my speed? do you guys think it may be the router? another thing, when i go to play at the local computer shop for lan parties, they have the same speed dsl i have, we can have 2 guys on final fantasy 11, 2-3 on everquest and me and someone else on half life 2 with no slowdown. i can download something and it stays at 50-55 Kb/s over there with all that going on. tonight my brother was on call of duty and i was downloading something from a site and my speed dropped down to 23kb/s and his game started lagging. what in the world happened? we are only 2 people using the net, compared to 6-8 over there. i install a router and everything starts going slower. i haven't configured the router, i just plugged it up. isn't that what i'm supposed to do?

i have adsl....should i have my router set to dynamic ip address, static ip address, or PPPoE? dlink says the pppoe is for most dsl users. my isp hasn't given me a user name or anything so i don't think i use PPPoE.

is there any tips on keeping the speeds up or something else i can download to test the speeds? thanks a lot.

Set your NICs to 100/full. You might have a problem with the duplex on one of your computers. You might want to remove the router to do some testing with the speeds one on one with a PC just to make sure the DSl connection is staying up.
If someone gets on your phone while on the DSL that can cause problems if your lines are old, signals are off, or you have a problem outside your house at the 'head' which is where your phone line from your house/apartment connects into the actual phone company's lines.

Riser