Set up my wireless network, what router, what networkcard in my laptop

Hey all,

I have a couple of questions about networking and wireless network, because I don't know much on this subject...

Lets start with my internet: I have a cable coming out of the wall, that leads to a router (DI-624+) From which 3 cables go to my 3 desktops

Now the DI-624+ also has wireless connection

So now, I'm planning to buy a new laptop, but I will mainly use it in my room (upstairs, so I can't connect it with a cable)

So I will have to use wireless, but there are some problems:

When I use a laptop upstairs, I have a good connection, but each 3 minutes or so, the connection is interupted for like 1 second, causing games and other stuff to dc
So I think it is pretty unstable

Also, I think my desktops internet is not on full speed, because when I use wireless on a laptop it's actually faster then on my desktops O.o, is this because of the router?

What causes this? Should I buy a new router and which one?

And also for my future new laptop: what type of network card or something should it have?

Thanks!

dlink 855 router...and a dlink wireless n adapter for your labtop...i have this running right now with 3 wireless devices and 2 wired.i lose a connection maybe once a month!this router runs 2 bands at once choose 2.4 or 5 ghz.i use 2.4 for the net and 5.0 for my sons wii!