My apologies if I am telling anyone what they already know. Upgrading equipment without knowing exactly why is a waste. If your current router is secure ( separate issue) why upgrade if you can get better speed for free?
As saab and hellsbrink mention, location is everything with wifi. It's all about the signal strength and quality. That is, how often the link is broken and has to be re-established. All those precious milliseconds of our lives down the drain as we wait for renegotiations . . .
In addition to some other good suggestions you may wish to download a program for your machine that gives audio feedback of signal strength as well as information about neighbouring interference. This will help you avoid dead spots. (Kismac for the Mac, Netstumbler for a PC box or wiki-it-out-yerself for linux).
Part of "location" is the antenna/e that you are using. Propagation patterns are obviously dependent on your antenna and it's orientation. I like to survey with a small 12-15cm and large 25-35cm antenna. Try vertical and horizontal orientations. If you are using your laptop's internal antennae find out where they are located. Then you can walk around like an asylum patient holding you laptop in different orientations.
After you get a feel for the propagation in you environment you can try adding some reflectors to your access point. There are some very ugly looking ones here:
Parabolic Templat
But they probably do the job. I found that a carefully built 40x30cm sized parabolic reflector and a "9 dB" 30 cm whip antenna eliminated hot and dead spots at the very edge of rated coverage. The area of the box parabola aperture is supposed to be equivalent to the area of a parabolic dish antenna. So a 30x40 recangular aperture is theoretically the same as a 38cm diameter dish antenna. Not bad for a "Tesco" freebee.
For longer range:
Long Range Wi-fi Dish Antenna by dxzone.com
For the interested reader:
VHF UHF Ant
Have fun and be nice your dog.
Hooroo!