WRT54G2 Wireless Connection Disconnects

First thing, do you live far away from others or do you live in an apartment? These days, there are so many people using that band that I'm surprised it works for anyone. It is especially true if this is the sort of place where everyone has a microwave, because they are in the same band and they leak, just a little.
Second, does your AP has a frequency that is unique? There is a "survey" button that tells you who else is using wi-fi in the area and on what frequency. You should use your own frequency, away from others, if you can.
Finally, do you have a good strong signal? If you do not, your throughput will never be as good or reliable. Using an aftermarket antenna MAY help.
Finally, it could be an issue in the Mac. Check driver levels for your wi-fi hardware, insure you have the latest. Search for wi-fi problems using your model number, or give Apple a call to see if there are known problems. Make sure you have the latest firmware on your Macbook too.
Now, I think you are telling me that you have tried running the same aps when you were wired in to your AP rather than using it by Wi-Fi and the same aps used in the same way, don't fail. That is the first thing I'd try. And if that was the case, aps work when wired and fail when you use wi-fi, I'd do the above.
(And you do not live near an airport (radar), and none of your neighbors are hams that do high frequency experimentation.)
The wi-fi devices are FCC Part 15 devices, using low powered transmissions on frequency bands that are actually licensed to other services. For example, some of the channels are on a ham band. It is possible that a Ham radio operator would do high power transmissions on a frequency shared with wi-fi and knock hundreds of APs out of service for a short time. Part of the rules that part 15 devices live by is that since they are unlicensed guests, the people who are actually licensed for the bands have priority and you are the one who has to deal with the interference.
But we have no indication, other than the intermittent nature of the problem, that you have an interference problem at all. And it seems more traffic related than time related, although the other rule of network failures is that you notice the failures that happen while you are using the network and you don't see the ones that happen when you are not using the net - could be failing all the time and you would never see the failures - other than the ones that happened while you were using the network heavily.
There are techs who own spectrum analyzers who can make a better guess at this sort of thing than I can, but my guess is that you do not want to pay them for this answer.
Good Luck!