Soon, I will be moving into a converted garage that is currently outside the range of our wireless router. (linksys G)
I can't move the location of the wireless router due to cable locations. I believe I need the signal to travel another 40 feet or so and through 2 walls. Would it be better to buy a new N router, or just get a wireless repeater? My laptop has an N card in it.
Also, I saw these come highly recommended from newegg, is this the type of equipment I would need to extend my current signal?
Well there are many factors to decide upon to solve a range issue. You have to consider interference from other 2.4 ghz networks as well as what the walls are made of that you are trying to transmit through. There is also the required bandwidth. I highly doubt that the wireless adapter in you notebook could transmit back 40 ft passed where your g signal ends.
A repeater might do the job but your bandwidth suffers. A perfect G connection gets about 12 mb/s in real life and with a repeater you will be lucky to get 6 mb/s and at the range your talking you'll be lucky to get 3 mb/s.
Refurbed N networking equipment is fairly cheap nowadays so what I would do is pick up two cisco refurbed e2000 routers on Amazon for $40 and flash them both with Tomato USB. i would then run an ethernet cable as close as I could from the G router to the garage plug it into the first e2000 and set it up as a wireless access point. I would then set up the second router as a wireless to wired bridge. You would have to wire your notebook in the garage but the connection would have much more bandwidth. In my apartment with the 5 ghz band I get 50 mb/s through two walls at 25'. You may have to use the 2.4 ghz band to get more range but with less bandwidth. You can flash the second router with DD-WRT and also set it up as a repeater so you don't have to wire in your notebook but this is more complicated and cuts your bandwidth in half.
I realize this is a much more complicated solution, but it will give you the best results in terms of range and speed at a similar price point.
A note about tomato wireless to wired bridges is that they set up a separate NAT so you cannot windows file share with the computers on the Linksys G network. You should use DD-WRT on the second router to avoid this. If you don't windows file share I wouldn't worry about it. DD-WRT is bit less user friendly with the user interface and the install so I try to steer people away from it unless there is not way around it.